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Fun with wav
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< p > < span class = "sc" > < abbr title = "Too long; don't read" > tl;dr< / abbr > : < / span > Playing to process a < code > wav< / code > file. < code > C< / code > was easier and cleaner than Ruby.< / p >
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< p > I had to calculate the sum of the absolute value of datas of a < code > .wav< / code > file.
For efficiency (and fun) reasons, I had chosen < code > C< / code > language.< / p >
< p > It was a long time I didn’ t used < code > C< / code > .
From my memory it was a pain to read and write to files.
But I was really impressed by how clean the code is.
And it is even more impressive knowing I used mostly low level functions.< / p >
< p > A < code > wav< / code > file has an header containing many meta-datas.
This header was optimized to take the less space possible.
Therefore, header is thinked with Bytes.< / p >
< ul >
< li > The 4th first Bytes must contains < code > RIFF< / code > in ASCII,< / li >
< li > the following 4th Bytes is an 32 bits integer giving the size of the file minus 8, etc… < / li >
< / ul >
< p > Surprisingly, I believe read this kind of file with a higher level language would have more difficult than in < code > C< / code > .
Proof: I only have to search on the web the complete header format and write it in a struct.< / p >
< pre class = "twilight" >
< span class = "Storage" > struct< / span > wavfile
{
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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 >
< 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 >
< span class = "Support" > int32_t< / span > bytes_per_second;
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< span class = "Support" > int16_t< / span > bytes_by_capture;
< span class = "Support" > int16_t< / span > bits_per_sample;
< 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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};
< / pre >
< p > If I had to read it in Ruby (for example), I believe I’ d had to write a read entry for each bloc value.
But in < code > C< / code > I simply written:< / p >
< pre class = "twilight" >
< span class = "SupportFunction" > fread< / span > (& header,< span class = "Keyword" > sizeof< / span > (header),< span class = "Constant" > 1< / span > ,wav);
< / pre >
< p > Only one step to fill my data structure. Magic!< / p >
< p > Then, get an int value coded on two Bytes is also not a natural operation for high level language.
In < code > C< / code > , to read a sequence of 2 Bytes numbers I only had to write:< / p >
< pre class = "twilight" >
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< span class = "Support" > int16_t< / 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) ) {
< span class = "Comment" > < span class = "Comment" > //< / span > do something with value< / span >
}
< / pre >
< p > Finally I ended with the following code. Remark I know the wav format (16 bit / 48000Hz):< / p >
< 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" >
< pre class = "twilight" >
< span class = "CCCPreprocessorLine" > #< span class = "CCCPreprocessorDirective" > include< / span > < span class = "String" > < span class = "String" > < < / span > stdio.h< span class = "String" > > < / span > < / span > < / span >
< 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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< 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 >
< 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 >
< span class = "Support" > int32_t< / span > bytes_per_second;
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< span class = "Support" > int16_t< / span > bytes_by_capture;
< span class = "Support" > int16_t< / span > bits_per_sample;
< 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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};
< 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[]) {
< span class = "Storage" > char< / span > *filename=argv[< span class = "Constant" > 1< / span > ];
FILE *wav = < span class = "SupportFunction" > fopen< / span > (filename,< span class = "String" > < span class = "String" > " < / span > rb< span class = "String" > " < / span > < / span > );
< span class = "Storage" > struct< / span > wavfile header;
< span class = "Keyword" > if< / span > ( wav == < span class = "Constant" > NULL< / span > ) {
< 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);
< span class = "SupportFunction" > exit< / span > (< span class = "Constant" > 1< / span > );
}
< 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 file header< span class = "StringConstant" > \n< / span > < span class = "String" > " < / span > < / span > );
< span class = "SupportFunction" > exit< / span > (< span class = "Constant" > 1< / span > );
}
< 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 >
|| header.id[< span class = "Constant" > 1< / span > ] != < span class = "String" > < span class = "String" > '< / span > I< span class = "String" > '< / span > < / span >
|| header.id[< span class = "Constant" > 2< / span > ] != < span class = "String" > < span class = "String" > '< / span > F< span class = "String" > '< / span > < / span >
|| header.id[< span class = "Constant" > 3< / span > ] != < span class = "String" > < span class = "String" > '< / span > F< span class = "String" > '< / span > < / span > ) {
< 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 > );
< 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 > sum=< span class = "Constant" > 0< / span > ;
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< span class = "Support" > int16_t< / 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) ) {
< span class = "Comment" > < span class = "Comment" > //< / span > fprintf(stderr," %d\n" , value);< / span >
< 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" > %ld< / 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 > Of course it is only a hack.
But we can see how easy and clean it should be to improve.
As I say often: the right tool for your need instead of the same tool for all your needs.
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 > int32_t< / code > instead of < code > int< / code > .< / em > < / p >
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Created: 10/14/2010
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Modified: 10/15/2010
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