Commit ef2fa1d9 authored by Thomas Schmitt's avatar Thomas Schmitt

Adapting to surplus chunks and subchunks in .wav files

parent b5b5cc1f
#define Cdrskin_timestamP "2017.09.16.105713"
#define Cdrskin_timestamP "2017.12.31.111507"
Sound extraction for CD-DA burning from .WAV audio file format
Using information and text snippets
from https://ccrma.stanford.edu/courses/422/projects/WaveFormat/
in may 2013. The link is now dead. An apparent copy of the page
is 2017 at: http://soundfile.sapp.org/doc/WaveFormat/
from https://en.wikipedia.org/wiki/WAV
For libburnia-project.org by Thomas Schmitt <scdbackup@gmx.net>
December 2017
The WAVE file format is an application of the Microsoft RIFF container format
for multimedia files. A RIFF file consists of Chunks which contain Subchunks.
The Chunks form a linked list within the file, the Subchunks form a linked
list inside their Chunk.
All numbers are stored in little-endian byte order.
A .WAV file consists at least of one Chunk with id "RIFF", which contains
one Subchunk with id "fmt " and one with id "data":
Offset Size Name Description
0 4 ChunkID Contains the letters "RIFF"
4 4 ChunkSize The size of the rest of the chunk following
this field. I.e. the two fields ChunkID and
ChunkSize are not included in this count.
8 4 Format Contains the letters "WAVE"
The "fmt " subchunk describes the sound data's format:
Offset Size Name Description
0 4 Subchunk1ID Contains the letters "fmt "
4 4 Subchunk1Size The size of the rest of the Subchunk following
this field. I.e. Subchunk1ID and Subchunk1Size
are not included in this count.
8 2 AudioFormat PCM = 1 (i.e. Linear quantization)
Values other than 1 indicate some
form of compression.
10 2 NumChannels Mono = 1, Stereo = 2, etc.
12 4 SampleRate 8000, 44100, etc.
16 4 ByteRate == SampleRate * NumChannels * BitsPerSample/8
20 2 BlockAlign == NumChannels * BitsPerSample/8
The number of bytes for one sample including
all channels.
22 2 BitsPerSample 8 bits = 8, 16 bits = 16, etc.
More data may follow in this Subchunk if AudioFormat is not PCM.
The "data" subchunk contains the size of the data and the actual sound:
Offset Size Name Description
0 4 Subchunk2ID Contains the letters "data"
4 4 Subchunk2Size == NumSamples * NumChannels * BitsPerSample/8
The number of audio data bytes.
8 * Data The audio data bytes.
CD-DA prescribes these "fmt " parameters:
AudioFormat == 1
SampleRate == 44100
BitsPerSample == 16
NumChannels == 2 (stereo)
(little-endian byte order)
If matching parameters are given in the .WAV file, one can directly use the
data bytes of Subchunk "data" as payload for burning a CD-DA track.
Above simple form can be expanded by other Chunks or Subchunks of Chunk "RIFF".
A .wav file appeared which beared a Subchunk "LIST" inside Chunk "RIFF".
Wikipedia mentions Chunks "INFO", "CSET", "JUNK", "PAD ".
Therefore one should expect such Chunks before Chunk "RIFF" and Subchunks
other than "fmt " and "data" inside the "RIFF" Chunk.
Multiple Chunks "RIFF" and Subchunks "fmt " or "data" per file have not been
seen yet. They would make extraction more cumbersome.
......@@ -55,6 +55,7 @@ int libdax_audioxtr_new(struct libdax_audioxtr **xtr, char *path, int flag)
o->bits_per_sample= 0;
o->msb_first= 0;
o->wav_data_location= 44;
o->wav_subchunk2_size= 0;
o->au_data_location= 0;
......@@ -121,47 +122,123 @@ static int libdax_audioxtr_open(struct libdax_audioxtr *o, int flag)
return(1);
}
/* @param flag: bit0= sequential file, skip by reading data
*/
static int libdax_audioxtr_skip(struct libdax_audioxtr *o,
off_t *old_pos,
off_t pos, int flag)
{
int ret;
size_t to_read;
static char buf[256]; /* Thread safe because the content does not matter */
if((flag & 1) || o->fd == 0) { /* stdin */
while(pos - *old_pos > 0) {
to_read= pos - *old_pos;
if(to_read > sizeof(buf))
to_read= sizeof(buf);
ret= read(o->fd, buf, to_read);
if(ret < (int) to_read)
return(0);
*old_pos+= to_read;
}
} else {
ret= lseek(o->fd, pos, SEEK_SET);
if(ret == -1)
return(0);
*old_pos= pos;
}
return(1);
}
static int libdax_audioxtr_identify_wav(struct libdax_audioxtr *o, int flag)
{
int ret;
char buf[45];
int ret, fmt_seen= 0, data_seen= 0;
off_t pos= 0, old_pos= 0, riff_end= 0;
char buf[16];
unsigned char *ubuf;
/* check wether this is a MS WAVE file .wav */
/* info used: http://ccrma.stanford.edu/courses/422/projects/WaveFormat/ */
if(o->fd!=0) {
ret= lseek(o->fd,0,SEEK_SET);
if(ret==-1)
/* info used: http://ccrma.stanford.edu/courses/422/projects/WaveFormat/
https://en.wikipedia.org/wiki/WAV
see summary in: doc/waveformat.txt
*/
ubuf= (unsigned char *) buf;
/* Look for ChunkID "RIFF" , tolerate other known chunks */
while(1) {
ret= libdax_audioxtr_skip(o, &old_pos, pos, 0);
if(ret <= 0)
return(0);
}
ret= read(o->fd, buf, 44);
if(ret<44)
ret= read(o->fd, buf, 8);
if(ret < 8)
return(0);
old_pos+= 8;
pos= old_pos + libdax_audioxtr_to_int(o, ubuf + 4, 4, 0);
if(pos > 0xffffffff || pos - old_pos < 4) /* Too large or no Format word */
return(0);
if(strncmp(buf, "RIFF", 4) == 0)
break;
/* Wikipedia mentions these known ChunkId values */
if(strncmp(buf, "INFO", 4) == 0 ||
strncmp(buf, "CSET", 4) == 0 ||
strncmp(buf, "JUNK", 4) == 0 ||
strncmp(buf, "PAD ", 4) == 0)
continue;
return(0);
buf[44]= 0; /* as stopper for any string operations */
}
if(strncmp(buf,"RIFF",4)!=0) /* ChunkID */
return(0);
if(strncmp(buf+8,"WAVE",4)!=0) /* Format */
/* Read RIFF Format header */
ret= read(o->fd, buf, 4);
if(ret < 4)
return(0);
if(strncmp(buf+12,"fmt ",4)!=0) /* Subchunk1ID */
return(0);
if(buf[16]!=16 || buf[17]!=0 || buf[18]!=0 || buf[19]!=0) /* Subchunk1Size */
return(0);
if(buf[20]!=1 || buf[21]!=0) /* AudioFormat must be 1 (Linear quantization) */
old_pos+= 4;
if(strncmp(buf, "WAVE", 4) != 0) /* Format */
return(0);
riff_end= pos;
strcpy(o->fmt,".wav");
o->msb_first= 0;
o->num_channels= libdax_audioxtr_to_int(o,(unsigned char *) buf+22,2,0);
o->sample_rate= libdax_audioxtr_to_int(o,(unsigned char *) buf+24,4,0);
o->bits_per_sample= libdax_audioxtr_to_int(o,(unsigned char *)buf+34,2,0);
sprintf(o->fmt_info,
".wav , num_channels=%d , sample_rate=%d , bits_per_sample=%d",
o->num_channels,o->sample_rate,o->bits_per_sample);
o->wav_subchunk2_size= libdax_audioxtr_to_int(o,(unsigned char *)buf+40,4,0);
o->data_size= o->wav_subchunk2_size;
return(1);
/* Look for SubchunkID "fmt " and "data" */
pos= old_pos;
while(old_pos < riff_end) {
ret= libdax_audioxtr_skip(o, &old_pos, pos, 0);
if(ret <= 0)
return(0);
ret= read(o->fd, buf, 8);
if(ret < 8)
return(0);
old_pos= pos + 8;
pos= old_pos + libdax_audioxtr_to_int(o, ubuf + 4, 4, 0); /* SubchunkSize */
if(strncmp(buf,"fmt ", 4) == 0) {
if(pos - old_pos < 16)
return(0);
ret= read(o->fd, buf, 16);
if(ret < 16)
return(0);
old_pos+= 16;
if(buf[0]!=1 || buf[1]!=0) /* AudioFormat (1 = Linear quantization) */
return(0);
o->msb_first= 0;
o->num_channels= libdax_audioxtr_to_int(o, ubuf + 2 , 2, 0);
o->sample_rate= libdax_audioxtr_to_int(o, ubuf + 4, 4, 0);
o->bits_per_sample= libdax_audioxtr_to_int(o, ubuf + 14, 2, 0);
sprintf(o->fmt_info,
".wav , num_channels=%d , sample_rate=%d , bits_per_sample=%d",
o->num_channels, o->sample_rate, o->bits_per_sample);
fmt_seen= 1;
} else if(strncmp(buf,"data", 4) == 0) {
o->wav_data_location= old_pos;
o->wav_subchunk2_size= pos - old_pos;
o->data_size= o->wav_subchunk2_size;
data_seen= 1;
}
if(fmt_seen && data_seen) {
strcpy(o->fmt,".wav");
return(1);
}
}
return(0);
}
......@@ -256,7 +333,7 @@ static int libdax_audioxtr_init_reading(struct libdax_audioxtr *o, int flag)
o->extract_count= 0;
if(strcmp(o->fmt,".wav")==0)
ret= lseek(o->fd,44,SEEK_SET);
ret= lseek(o->fd, o->wav_data_location, SEEK_SET);
else if(strcmp(o->fmt,".au")==0)
ret= lseek(o->fd,o->au_data_location,SEEK_SET);
else
......
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