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522 lines
No EOL
36 KiB
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<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="fr" xml:lang="fr">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<link rel="shortcut icon" type="image/x-icon" href="/Scratch/img/favicon.ico" />
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<link rel="alternate" type="application/rss+xml" title="RSS" href="http://feeds.feedburner.com/yannespositocomen"/>
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<link rel="alternate" lang="fr" xml:lang="fr" title="S'amuser avec un .wav" type="text/html" hreflang="fr" href="/Scratch/fr/blog/2010-10-14-Fun-with-wav/" />
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<link rel="alternate" lang="en" xml:lang="en" title="Fun with wav" type="text/html" hreflang="en" href="/Scratch/en/blog/2010-10-14-Fun-with-wav/" />
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<script type="text/javascript" src="/Scratch/js/jquery-1.3.1.min.js"></script>
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<![endif]-->
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<script type="text/javascript" src="/Scratch/js/MathJax/MathJax.js"></script>
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< % end %>
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-->
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<title>Fun with wav</title>
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</head>
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<body lang="en">
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<script type="text/javascript">// <![CDATA[
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document.write('<div id="blackpage"><img src="/Scratch/img/loading.gif" alt="loading..."/></div>');
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// ]]>
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</script>
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<div id="content">
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<div id="choix">
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<div class="return"><a href="#entete">↓ Menu ↓</a></div>
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<a href="/Scratch/fr/blog/2010-10-14-Fun-with-wav/" onclick="setLanguage('fr')">en Français</a>
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</div>
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</div>
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<img src="/Scratch/img/presentation.png" alt="Presentation drawing"/>
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<div id="titre">
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<h1>
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Fun with wav
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</h1>
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</div>
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<div class="flush"></div>
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<div class="flush"></div>
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<div id="afterheader">
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<div class="corps">
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<div class="intro">
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<p><span class="sc"><abbr title="Too long; don't read">tl;dr</abbr>: </span> Played to process a <code>wav</code> file. <code>C</code> was easier and cleaner than Ruby.</p>
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<p>edit: I wanted this program to work only on one specific machine (a x86 on a 32 bit Ubuntu). Therefore I didn’t had any portability consideration. This is only a <em>hack</em>.</p>
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</div>
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<p>I had to compute the sum of the absolute values of data of a <code>.wav</code> file.
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For efficiency (and fun) reasons, I had chosen <code>C</code> language.</p>
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<p>I didn’t programmed in <code>C</code> for a long time.
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From my memory it was a pain to read and write to files.
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But in the end I was really impressed by the code I get.
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It was really clean.
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This is even more impressive knowing I used mostly low level functions.</p>
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<p>A <code>wav</code> file has an header containing many metadata.
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This header was optimized to take as few space as possible.
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The header is then a block of packed bytes.</p>
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<ul>
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<li>The 4th first bytes must contains <code>RIFF</code> in ASCII,</li>
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<li>the following 4th Bytes is an 32 bits integer giving the size of the file minus 8, etc…</li>
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</ul>
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<p>Surprisingly, I believe that reading this kind of file is easier in <code>C</code> than in most higher level language.
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Proof: I only have to search on the web the complete header format and write it in a struct.</p>
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<pre class="twilight">
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<span class="Storage">struct</span> wavfile
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{
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<span class="Storage">char</span> id[<span class="Constant">4</span>]; <span class="Comment"><span class="Comment">//</span> should always contain "RIFF"</span>
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<span class="Storage">int</span> totallength; <span class="Comment"><span class="Comment">//</span> total file length minus 8</span>
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<span class="Storage">char</span> wavefmt[<span class="Constant">8</span>]; <span class="Comment"><span class="Comment">//</span> should be "WAVEfmt "</span>
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<span class="Storage">int</span> format; <span class="Comment"><span class="Comment">//</span> 16 for PCM format</span>
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<span class="Storage">short</span> pcm; <span class="Comment"><span class="Comment">//</span> 1 for PCM format</span>
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<span class="Storage">short</span> channels; <span class="Comment"><span class="Comment">//</span> channels</span>
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<span class="Storage">int</span> frequency; <span class="Comment"><span class="Comment">//</span> sampling frequency</span>
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<span class="Storage">int</span> bytes_per_second;
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<span class="Storage">short</span> bytes_by_capture;
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<span class="Storage">short</span> bits_per_sample;
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<span class="Storage">char</span> data[<span class="Constant">4</span>]; <span class="Comment"><span class="Comment">//</span> should always contain "data"</span>
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<span class="Storage">int</span> bytes_in_data;
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};
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</pre>
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<p>To read this kind of data in Ruby, I certainly had to write a block of code for each element in the struct.
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But in <code>C</code> I simply written:</p>
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<pre class="twilight">
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<span class="SupportFunction">fread</span>(&header,<span class="Keyword">sizeof</span>(header),<span class="Constant">1</span>,wav)
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</pre>
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<p>Only one step to fill my data structure. Magic!</p>
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<p>Then, get an int value coded on two Bytes is also not a natural operation for high level language.
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In <code>C</code>, to read a sequence of 2 Bytes numbers I only had to write:</p>
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<pre class="twilight">
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<span class="Storage">short</span> value=<span class="Constant">0</span>;
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<span class="Keyword">while</span>( <span class="SupportFunction">fread</span>(&value,<span class="Keyword">sizeof</span>(value),<span class="Constant">1</span>,wav) ) {
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<span class="Comment"><span class="Comment">//</span> do something with value</span>
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}
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</pre>
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<p>Finally I ended with the following code. Remark I know the wav format (16 bit / 48000Hz):</p>
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<div class="code"><div class="file"><a href="/Scratch/en/blog/2010-10-14-Fun-with-wav/code/wavsum.c"> ➥ wavsum.c </a></div><div class="withfile">
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<pre class="twilight">
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<span class="CCCPreprocessorLine">#<span class="CCCPreprocessorDirective">include</span> <span class="String"><span class="String"><</span>stdio.h<span class="String">></span></span></span>
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<span class="CCCPreprocessorLine">#<span class="CCCPreprocessorDirective">include</span> <span class="String"><span class="String"><</span>stdlib.h<span class="String">></span></span></span>
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<span class="CCCPreprocessorLine">#<span class="CCCPreprocessorDirective">include</span> <span class="String"><span class="String"><</span>stdint.h<span class="String">></span></span></span>
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<span class="Storage">struct</span> wavfile
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{
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<span class="Storage">char</span> id[<span class="Constant">4</span>]; <span class="Comment"><span class="Comment">//</span> should always contain "RIFF"</span>
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<span class="Storage">int</span> totallength; <span class="Comment"><span class="Comment">//</span> total file length minus 8</span>
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<span class="Storage">char</span> wavefmt[<span class="Constant">8</span>]; <span class="Comment"><span class="Comment">//</span> should be "WAVEfmt "</span>
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<span class="Storage">int</span> format; <span class="Comment"><span class="Comment">//</span> 16 for PCM format</span>
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<span class="Storage">short</span> pcm; <span class="Comment"><span class="Comment">//</span> 1 for PCM format</span>
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<span class="Storage">short</span> channels; <span class="Comment"><span class="Comment">//</span> channels</span>
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<span class="Storage">int</span> frequency; <span class="Comment"><span class="Comment">//</span> sampling frequency</span>
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<span class="Storage">int</span> bytes_per_second;
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<span class="Storage">short</span> bytes_by_capture;
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<span class="Storage">short</span> bits_per_sample;
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<span class="Storage">char</span> data[<span class="Constant">4</span>]; <span class="Comment"><span class="Comment">//</span> should always contain "data"</span>
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<span class="Storage">int</span> bytes_in_data;
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};
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<span class="Storage">int</span> <span class="Entity">ma<span class="Entity">in</span></span>(<span class="Storage">int</span> argc, <span class="Storage">char</span> *argv[]) {
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<span class="Storage">char</span> *filename=argv[<span class="Constant">1</span>];
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FILE *wav = <span class="SupportFunction">fopen</span>(filename,<span class="String"><span class="String">"</span>rb<span class="String">"</span></span>);
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<span class="Storage">struct</span> wavfile header;
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<span class="Keyword">if</span> ( wav == <span class="Constant">NULL</span> ) {
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>Can't open input file <span class="StringConstant">%s</span><span class="String">"</span></span>, filename);
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<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
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}
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<span class="Comment"><span class="Comment">//</span> read header</span>
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<span class="Keyword">if</span> ( <span class="SupportFunction">fread</span>(&header,<span class="Keyword">sizeof</span>(header),<span class="Constant">1</span>,wav) < <span class="Constant">1</span> )
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{
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>Can't read file header<span class="StringConstant">\n</span><span class="String">"</span></span>);
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<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
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}
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<span class="Keyword">if</span> ( header.id[<span class="Constant">0</span>] != <span class="String"><span class="String">'</span>R<span class="String">'</span></span>
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|| header.id[<span class="Constant">1</span>] != <span class="String"><span class="String">'</span>I<span class="String">'</span></span>
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|| header.id[<span class="Constant">2</span>] != <span class="String"><span class="String">'</span>F<span class="String">'</span></span>
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|| header.id[<span class="Constant">3</span>] != <span class="String"><span class="String">'</span>F<span class="String">'</span></span> ) {
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>ERROR: Not wav format<span class="StringConstant">\n</span><span class="String">"</span></span>);
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<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
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}
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>wav format<span class="StringConstant">\n</span><span class="String">"</span></span>);
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<span class="Comment"><span class="Comment">//</span> read data</span>
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<span class="Storage">long</span> sum=<span class="Constant">0</span>;
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<span class="Storage">short</span> value=<span class="Constant">0</span>;
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<span class="Keyword">while</span>( <span class="SupportFunction">fread</span>(&value,<span class="Keyword">sizeof</span>(value),<span class="Constant">1</span>,wav) ) {
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<span class="Comment"><span class="Comment">//</span> fprintf(stderr,"%d\n", value);</span>
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<span class="Keyword">if</span> (value<<span class="Constant">0</span>) { value=-value; }
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sum += value;
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}
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<span class="SupportFunction">printf</span>(<span class="String"><span class="String">"</span><span class="StringConstant">%ld</span><span class="StringConstant">\n</span><span class="String">"</span></span>,sum);
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<span class="SupportFunction">exit</span>(<span class="Constant">0</span>);
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}
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</pre>
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</div></div>
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<p>Of course it is only a hack.
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But we can see how easy and clean it should be to improve.
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As I say often: the right tool for your need instead of the same tool for all your needs.
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Because here <code>C</code> is clearly far superior than Ruby to handle this simple tasks.</p>
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<p>I am curious to know if somebody know a nice way to do this with Ruby or Python.</p>
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<p><em>edit: for compatibility reasons (64bit machines) used <code>int16_t</code> instead of <code>short</code> and <code>int</code> instead of <code>int</code>.</em></p>
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<div class="intro">
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<p>Edit (2): after most consideration about portability I made an <em>hopefully</em> more portable version.
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But I must confess this task was a bit tedious.
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The code remain as readable as before.
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But I had to use some compiler specific declaration to force the structure to be packed:</p>
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<pre class="twilight">
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__attribute__((__packed__))
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</pre>
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<p>Therefore this implementation should for big and little endian architecture.
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However, it must be compiled with <code>gcc</code>.
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The new code make more tests but still don’t use <code>mmap</code>.
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Here it is:</p>
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</div>
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<div class="code"><div class="file"><a href="/Scratch/en/blog/2010-10-14-Fun-with-wav/code/wavsum2.c"> ➥ wavsum2.c </a></div><div class="withfile">
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<pre class="twilight">
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<span class="CCCPreprocessorLine">#<span class="CCCPreprocessorDirective">include</span> <span class="String"><span class="String"><</span>stdio.h<span class="String">></span></span></span>
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<span class="CCCPreprocessorLine">#<span class="CCCPreprocessorDirective">include</span> <span class="String"><span class="String"><</span>stdlib.h<span class="String">></span></span></span>
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<span class="CCCPreprocessorLine">#<span class="CCCPreprocessorDirective">include</span> <span class="String"><span class="String"><</span>string.h<span class="String">></span></span> </span><span class="Comment"><span class="Comment">//</span> for memcmp</span>
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<span class="CCCPreprocessorLine">#<span class="CCCPreprocessorDirective">include</span> <span class="String"><span class="String"><</span>stdint.h<span class="String">></span></span> </span><span class="Comment"><span class="Comment">//</span> for int16_t and int32_t</span>
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<span class="Storage">struct</span> wavfile
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{
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<span class="Storage">char</span> id[<span class="Constant">4</span>]; <span class="Comment"><span class="Comment">//</span> should always contain "RIFF"</span>
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<span class="Support">int32_t</span> totallength; <span class="Comment"><span class="Comment">//</span> total file length minus 8</span>
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<span class="Storage">char</span> wavefmt[<span class="Constant">8</span>]; <span class="Comment"><span class="Comment">//</span> should be "WAVEfmt "</span>
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<span class="Support">int32_t</span> format; <span class="Comment"><span class="Comment">//</span> 16 for PCM format</span>
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<span class="Support">int16_t</span> pcm; <span class="Comment"><span class="Comment">//</span> 1 for PCM format</span>
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<span class="Support">int16_t</span> channels; <span class="Comment"><span class="Comment">//</span> channels</span>
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<span class="Support">int32_t</span> frequency; <span class="Comment"><span class="Comment">//</span> sampling frequency</span>
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<span class="Support">int32_t</span> bytes_per_second;
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<span class="Support">int16_t</span> bytes_by_capture;
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<span class="Support">int16_t</span> bits_per_sample;
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<span class="Storage">char</span> data[<span class="Constant">4</span>]; <span class="Comment"><span class="Comment">//</span> should always contain "data"</span>
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<span class="Support">int32_t</span> bytes_in_data;
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} __attribute__((__packed__));
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<span class="Storage">int</span> is_big_endian(<span class="Storage">void</span>) {
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<span class="Storage">union</span> {
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<span class="Support">uint32_t</span> i;
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<span class="Storage">char</span> c[<span class="Constant">4</span>];
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} bint = {<span class="Constant">0x01000000</span>};
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<span class="Keyword">return</span> bint.c[<span class="Constant">0</span>]==<span class="Constant">1</span>;
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}
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<span class="Storage">int</span> <span class="Entity">ma<span class="Entity">in</span></span>(<span class="Storage">int</span> argc, <span class="Storage">char</span> *argv[]) {
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<span class="Storage">char</span> *filename=argv[<span class="Constant">1</span>];
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FILE *wav = <span class="SupportFunction">fopen</span>(filename,<span class="String"><span class="String">"</span>rb<span class="String">"</span></span>);
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<span class="Storage">struct</span> wavfile header;
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<span class="Keyword">if</span> ( wav == <span class="Constant">NULL</span> ) {
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>Can't open input file <span class="StringConstant">%s</span><span class="StringConstant">\n</span><span class="String">"</span></span>, filename);
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<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
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}
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<span class="Comment"><span class="Comment">//</span> read header</span>
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<span class="Keyword">if</span> ( <span class="SupportFunction">fread</span>(&header,<span class="Keyword">sizeof</span>(header),<span class="Constant">1</span>,wav) < <span class="Constant">1</span> ) {
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>Can't read input file header <span class="StringConstant">%s</span><span class="StringConstant">\n</span><span class="String">"</span></span>, filename);
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<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
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}
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<span class="Comment"><span class="Comment">//</span> if wav file isn't the same endianness than the current environment</span>
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<span class="Comment"><span class="Comment">//</span> we quit</span>
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<span class="Keyword">if</span> ( is_big_endian() ) {
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<span class="Keyword">if</span> ( <span class="SupportFunction">memcmp</span>( header.id,<span class="String"><span class="String">"</span>RIFX<span class="String">"</span></span>, <span class="Constant">4</span>) != <span class="Constant">0</span> ) {
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>ERROR: <span class="StringConstant">%s</span> is not a big endian wav file<span class="StringConstant">\n</span><span class="String">"</span></span>, filename);
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<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
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}
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} <span class="Keyword">else</span> {
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<span class="Keyword">if</span> ( <span class="SupportFunction">memcmp</span>( header.id,<span class="String"><span class="String">"</span>RIFF<span class="String">"</span></span>, <span class="Constant">4</span>) != <span class="Constant">0</span> ) {
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>ERROR: <span class="StringConstant">%s</span> is not a little endian wav file<span class="StringConstant">\n</span><span class="String">"</span></span>, filename);
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<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
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}
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}
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<span class="Keyword">if</span> ( <span class="SupportFunction">memcmp</span>( header.wavefmt, <span class="String"><span class="String">"</span>WAVEfmt <span class="String">"</span></span>, <span class="Constant">8</span>) != <span class="Constant">0</span>
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|| <span class="SupportFunction">memcmp</span>( header.data, <span class="String"><span class="String">"</span>data<span class="String">"</span></span>, <span class="Constant">4</span>) != <span class="Constant">0</span>
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) {
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>ERROR: Not wav format<span class="StringConstant">\n</span><span class="String">"</span></span>);
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<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
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}
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<span class="Keyword">if</span> (header.format != <span class="Constant">16</span>) {
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<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span><span class="StringConstant">\n</span>ERROR: not 16 bit wav format.<span class="String">"</span></span>);
|
|
<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
|
|
}
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>format: <span class="StringConstant">%d</span> bits<span class="String">"</span></span>, header.format);
|
|
<span class="Keyword">if</span> (header.format == <span class="Constant">16</span>) {
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>, PCM<span class="String">"</span></span>);
|
|
} <span class="Keyword">else</span> {
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>, not PCM (<span class="StringConstant">%d</span>)<span class="String">"</span></span>, header.format);
|
|
}
|
|
<span class="Keyword">if</span> (header.pcm == <span class="Constant">1</span>) {
|
|
<span class="SupportFunction">fprintf</span>(stderr, <span class="String"><span class="String">"</span> uncompressed<span class="String">"</span></span> );
|
|
} <span class="Keyword">else</span> {
|
|
<span class="SupportFunction">fprintf</span>(stderr, <span class="String"><span class="String">"</span> compressed<span class="String">"</span></span> );
|
|
}
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>, channel <span class="StringConstant">%d</span><span class="String">"</span></span>, header.pcm);
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>, freq <span class="StringConstant">%d</span><span class="String">"</span></span>, header.frequency );
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>, <span class="StringConstant">%d</span> bytes per sec<span class="String">"</span></span>, header.bytes_per_second );
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>, <span class="StringConstant">%d</span> bytes by capture<span class="String">"</span></span>, header.bytes_by_capture );
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>, <span class="StringConstant">%d</span> bits per sample<span class="String">"</span></span>, header.bytes_by_capture );
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span><span class="StringConstant">\n</span><span class="String">"</span></span> );
|
|
|
|
<span class="Keyword">if</span> ( <span class="SupportFunction">memcmp</span>( header.data, <span class="String"><span class="String">"</span>data<span class="String">"</span></span>, <span class="Constant">4</span>) != <span class="Constant">0</span> ) {
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>ERROR: Prrroblem?<span class="StringConstant">\n</span><span class="String">"</span></span>);
|
|
<span class="SupportFunction">exit</span>(<span class="Constant">1</span>);
|
|
}
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>wav format<span class="StringConstant">\n</span><span class="String">"</span></span>);
|
|
|
|
<span class="Comment"><span class="Comment">//</span> read data</span>
|
|
<span class="Storage">long</span> <span class="Storage">long</span> sum=<span class="Constant">0</span>;
|
|
<span class="Support">int16_t</span> value;
|
|
<span class="Storage">int</span> i=<span class="Constant">0</span>;
|
|
<span class="SupportFunction">fprintf</span>(stderr,<span class="String"><span class="String">"</span>---<span class="StringConstant">\n</span><span class="String">"</span></span>, value);
|
|
<span class="Keyword">while</span>( <span class="SupportFunction">fread</span>(&value,<span class="Keyword">sizeof</span>(value),<span class="Constant">1</span>,wav) ) {
|
|
<span class="Keyword">if</span> (value<<span class="Constant">0</span>) { value=-value; }
|
|
sum += value;
|
|
}
|
|
<span class="SupportFunction">printf</span>(<span class="String"><span class="String">"</span><span class="StringConstant">%lld</span><span class="StringConstant">\n</span><span class="String">"</span></span>,sum);
|
|
<span class="SupportFunction">exit</span>(<span class="Constant">0</span>);
|
|
}
|
|
</pre>
|
|
</div></div>
|
|
|
|
<p><em>Edit(3)</em>:
|
|
On <a href="http://reddit.com">reddit</a>
|
|
<a href="http://www.reddit.com/user/Bogdanp">Bogdanp</a>
|
|
proposed a Python version:</p>
|
|
|
|
<div class="code"><div class="file"><a href="/Scratch/en/blog/2010-10-14-Fun-with-wav/code/wavsum.py"> ➥ wavsum.py </a></div><div class="withfile">
|
|
<pre class="twilight">
|
|
<span class="Comment"><span class="Comment">#</span>!/usr/bin/env python</span>
|
|
<span class="Keyword">from</span> struct <span class="Keyword">import</span> calcsize, unpack
|
|
<span class="Keyword">from</span> sys <span class="Keyword">import</span> argv, exit
|
|
|
|
<span class="Storage">def</span> <span class="Entity">word_iter</span>(<span class="Variable">f</span>):
|
|
<span class="Keyword">while</span> <span class="Constant">True</span>:
|
|
_bytes <span class="Keyword">=</span> f.read(<span class="Constant">2</span>)
|
|
|
|
<span class="Keyword">if</span> <span class="SupportFunction">len</span>(_bytes) <span class="Keyword">!=</span> <span class="Constant">2</span>:
|
|
<span class="Keyword">raise</span> <span class="Support">StopIteration</span>
|
|
|
|
<span class="Keyword">yield</span> unpack(<span class="String"><span class="String">"</span>=h<span class="String">"</span></span>, _bytes)[<span class="Constant">0</span>]
|
|
|
|
<span class="Keyword">try</span>:
|
|
<span class="Keyword">with</span> <span class="Support">open</span>(argv[<span class="Constant">1</span>], <span class="String"><span class="String">"</span>rb<span class="String">"</span></span>) <span class="Keyword">as</span> f:
|
|
wav <span class="Keyword">=</span> <span class="String"><span class="String">"</span>=4ci8cihhiihh4ci<span class="String">"</span></span>
|
|
wav_size <span class="Keyword">=</span> calcsize(wav)
|
|
metadata <span class="Keyword">=</span> unpack(wav, f.read(wav_size))
|
|
|
|
<span class="Keyword">if</span> <span class="String"><span class="String">"</span><span class="String"><span class="String">"</span></span></span>.join(metadata[:<span class="Constant">4</span>]) <span class="Keyword">!=</span> <span class="String"><span class="String">"</span>RIFF<span class="String">"</span></span>:
|
|
<span class="Keyword">print</span> <span class="String"><span class="String">"</span>error: not wav file.<span class="String">"</span></span>
|
|
exit(<span class="Constant">1</span>)
|
|
|
|
<span class="Keyword">print</span> <span class="SupportFunction">sum</span>(<span class="SupportFunction">abs</span>(word) <span class="Keyword">for</span> word <span class="Keyword">in</span> word_iter(f))
|
|
<span class="Keyword">except</span> <span class="Support">IOError</span>:
|
|
<span class="Keyword">print</span> <span class="String"><span class="String">"</span>error: can't open input file '<span class="StringConstant">%s</span>'.<span class="String">"</span></span> <span class="Keyword">%</span> argv[<span class="Constant">1</span>]
|
|
exit(<span class="Constant">1</span>)
|
|
</pre>
|
|
</div></div>
|
|
|
|
<p>and <a href="http://www.reddit.com/user/luikore">luikore</a>
|
|
proposed an impressive Ruby version:</p>
|
|
|
|
<div class="code"><div class="file"><a href="/Scratch/en/blog/2010-10-14-Fun-with-wav/code/wavsum.rb"> ➥ wavsum.rb </a></div><div class="withfile">
|
|
<pre class="twilight">
|
|
data <span class="Keyword">=</span> <span class="Variable">ARGF</span>.<span class="Entity">read</span>
|
|
keys <span class="Keyword">=</span> <span class="String"><span class="String">%w[</span>id totallength wavefmt format</span>
|
|
<span class="String"> pcm channels frequency bytes_per_second</span>
|
|
<span class="String"> bytes_by_capture bits_per_sample</span>
|
|
<span class="String"> data bytes_in_data sum</span>
|
|
<span class="String"> <span class="String">]</span></span>
|
|
values <span class="Keyword">=</span> data.<span class="Entity">unpack</span> <span class="String"><span class="String">'</span>Z4 i Z8 i s s i i s s Z4 i s*<span class="String">'</span></span>
|
|
sum <span class="Keyword">=</span> values.<span class="Entity">drop</span>(<span class="Constant">12</span>).<span class="Entity">map</span>(<span class="Keyword">&</span><span class="Constant"><span class="Constant">:</span>abs</span>).<span class="Entity">inject</span>(<span class="Constant"><span class="Constant">:</span>+</span>)
|
|
keys.<span class="Entity">zip</span>(values.<span class="Entity">take</span>(<span class="Constant">12</span>) <span class="Keyword"><<</span> sum) {|<span class="Variable">k</span>, <span class="Variable">v</span>|
|
|
puts <span class="String"><span class="String">"</span><span class="StringEmbeddedSource"><span class="StringEmbeddedSource">#{</span>k<span class="StringEmbeddedSource"><span class="StringEmbeddedSource">.</span><span class="Entity">ljust</span></span> <span class="StringConstant">17</span><span class="StringEmbeddedSource">}</span></span>: <span class="StringEmbeddedSource"><span class="StringEmbeddedSource">#{</span>v<span class="StringEmbeddedSource">}</span></span><span class="String">"</span></span>
|
|
}
|
|
</pre>
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</div></div>
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<div id="lastmod">
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Created: 10/14/2010
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Modified: 10/26/2010
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</div>
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<div>
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Entirely done with
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<a href="http://www.vim.org">Vim</a>
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and
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<a href="http://nanoc.stoneship.org">nanoc</a>
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<a href="/Scratch/en/validation/">Validation</a>
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<a href="http://validator.w3.org/check?uri=referer"> [xhtml] </a>
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.
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<a href="http://jigsaw.w3.org/css-validator/check/referer?profile=css3"> [css] </a>
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