Fun with wav
tl;dr: Playing to process a wav
file. C
was easier and cleaner than Ruby.
I had to calculate the sum of the absolute value of datas of a .wav
file.
For efficiency (and fun) reasons, I had chosen C
language.
It was a long time I didn’t used C
.
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.
A wav
file has an header containing many meta-datas.
This header was optimized to take the less space possible.
Therefore, header is thinked with Bytes.
- The 4th first Bytes must contains
RIFF
in ASCII, - the following 4th Bytes is an 32 bits integer giving the size of the file minus 8, etc…
Surprisingly, I believe read this kind of file with a higher level language would have more difficult than in C
.
Proof: I only have to search on the web the complete header format and write it in a struct.
struct wavfile { char id[4]; // should always contain "RIFF" int32_t totallength; // total file length minus 8 char wavefmt[8]; // should be "WAVEfmt " int32_t format; // 16 for PCM format int16_t pcm; // 1 for PCM format int16_t channels; // channels int32_t frequency; // sampling frequency int32_t bytes_per_second; int16_t bytes_by_capture; int16_t bits_per_sample; char data[4]; // should always contain "data" int32_t bytes_in_data; };
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 C
I simply written:
fread(&header,sizeof(header),1,wav);
Only one step to fill my data structure. Magic!
Then, get an int value coded on two Bytes is also not a natural operation for high level language.
In C
, to read a sequence of 2 Bytes numbers I only had to write:
int16_t value=0; while( fread(&value,sizeof(value),1,wav) ) { // do something with value }
Finally I ended with the following code. Remark I know the wav format (16 bit / 48000Hz):
#include <stdio.h> #include <stdlib.h> struct wavfile { char id[4]; // should always contain "RIFF" int32_t totallength; // total file length minus 8 char wavefmt[8]; // should be "WAVEfmt " int32_t format; // 16 for PCM format int16_t pcm; // 1 for PCM format int16_t channels; // channels int32_t frequency; // sampling frequency int32_t bytes_per_second; int16_t bytes_by_capture; int16_t bits_per_sample; char data[4]; // should always contain "data" int32_t bytes_in_data; }; int main(int argc, char *argv[]) { char *filename=argv[1]; FILE *wav = fopen(filename,"rb"); struct wavfile header; if ( wav == NULL ) { fprintf(stderr,"Can't open input file %s", filename); exit(1); } // read header if ( fread(&header,sizeof(header),1,wav) < sizeof(header) ) { fprintf(stderr,"Can't read file header\n"); exit(1); } if ( header.id[0] != 'R' || header.id[1] != 'I' || header.id[2] != 'F' || header.id[3] != 'F' ) { fprintf(stderr,"ERROR: Not wav format\n"); exit(1); } fprintf(stderr,"wav format\n"); // read data long sum=0; int16_t value=0; while( fread(&value,sizeof(value),1,wav) ) { // fprintf(stderr,"%d\n", value); if (value<0) { value=-value; } sum += value; } printf("%ld\n",sum); exit(0); }
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 C
is clearly far superior than Ruby to handle this simple tasks.
I am curious to know if somebody know a nice way to do this with Ruby or Python.
edit: for compatibility reasons (64bit machines) used int16_t
instead of short
and int32_t
instead of int
.