[alsa-devel] S24_LE is 3 bytes ? in alsa-lib example pcm.c
as far as I know: sample format S24_LE is 24bit sample in 4 bytes sample format S24_3LE is 24bit sample in 3 bytes (why else have separate definitions), right ?
In the ALSA-LIb example /test/pcm.c however (http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html) there is no diff between the 2 sample formats.
I noticed this by simply showing the bytes presented to snd_pcm_writei See:
S32_LE (for reference) ---------------------- ./pcm -c 2 -o S32_LE -f 4000 Playback device is plughw:0,0 Stream parameters are 48000Hz, S32_LE, 2 channels Sine wave rate is 4000.0000Hz Using transfer method: write write_loop: going to write: period_size=4096 samples data[00:31]= 00000000 00000000 ffffff3f ffffff3f a0ebd96e a0ebd96e ffffff7f ffffff7f data[32:63]= a0ebd96e a0ebd96e ffffff3f ffffff3f 00000000 00000000 010000c0 010000c0
S24_3LE (as expected) ---------------------- ./pcm -c 2 -o S24_3LE -f 4000 Playback device is plughw:0,0 Stream parameters are 48000Hz, S24_3LE, 2 channels Sine wave rate is 4000.0000Hz Using transfer method: write write_loop: going to write: period_size=4096 samples data[00:31]= 00000000 0000ffff 3fffff3f ead96eea d96effff 7fffff7f ead96eea d96effff data[32:63]= 3fffff3f 00000000 00000100 c00100c0 16269116 26910100 80010080 16269116
S24_LE ---------------------- ./pcm -c 2 -o S24_LE -f 4000 Playback device is plughw:0,0 Stream parameters are 48000Hz, S24_LE, 2 channels Sine wave rate is 4000.0000Hz Using transfer method: write write_loop: going to write: period_size=4096 samples data[00:31]= 00000000 0000ffff 3fffff3f ead96eea d96effff 7fffff7f ead96eea d96effff data[32:63]= 3fffff3f 00000000 00000100 c00100c0 16269116 26910100 80010080 16269116
I would expect to see data[00:31]= 0x00000000 00000000 00ffff3f 00ffff3f 00ebd96e 00ebd96e 00ffff7f 00ffff7f data[32:63]= 0x00ebd96e 00ebd96e 00ffff3f 00ffff3f 00000000 00000000 000000c0 000000c0 for S24_LE
do I miss something ? is this is a fault in /test/pcm.c ?
Norbert van Bolhuis wrote:
as far as I know: sample format S24_LE is 24bit sample in 4 bytes sample format S24_3LE is 24bit sample in 3 bytes (why else have separate definitions), right ?
Yes.
In the ALSA-LIb example /test/pcm.c however (http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html) there is no diff between the 2 sample formats.
That example program uses snd_pcm_format_width() although it should have used snd_pcm_format_physical_width() when calculating memory buffer sizes.
Regards, Clemens
On Thu, 10 Jul 2008, Clemens Ladisch wrote:
Norbert van Bolhuis wrote:
as far as I know: sample format S24_LE is 24bit sample in 4 bytes sample format S24_3LE is 24bit sample in 3 bytes (why else have separate definitions), right ?
Yes.
In the ALSA-LIb example /test/pcm.c however (http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html) there is no diff between the 2 sample formats.
That example program uses snd_pcm_format_width() although it should have used snd_pcm_format_physical_width() when calculating memory buffer sizes.
I think that the problem is in wrong area->step calculation in alsa-lib, but I'm still investigating where the real culprit is. The snd_pcm_format_width() is used only for sample filling (which is OK).
Jaroslav
----- Jaroslav Kysela perex@perex.cz Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc.
At Thu, 10 Jul 2008 12:19:05 +0200 (CEST), Jaroslav Kysela wrote:
On Thu, 10 Jul 2008, Clemens Ladisch wrote:
Norbert van Bolhuis wrote:
as far as I know: sample format S24_LE is 24bit sample in 4 bytes sample format S24_3LE is 24bit sample in 3 bytes (why else have separate definitions), right ?
Yes.
In the ALSA-LIb example /test/pcm.c however (http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html) there is no diff between the 2 sample formats.
That example program uses snd_pcm_format_width() although it should have used snd_pcm_format_physical_width() when calculating memory buffer sizes.
I think that the problem is in wrong area->step calculation in alsa-lib, but I'm still investigating where the real culprit is. The snd_pcm_format_width() is used only for sample filling (which is OK).
I think Clemens is right. The program uses snd_pcm_format_width() wrongly. Also, it won't work properly with strict aliasing...
Untested patch is below.
Takashi -- diff --git a/test/pcm.c b/test/pcm.c index cd29259..ecd0afa 100644 --- a/test/pcm.c +++ b/test/pcm.c @@ -38,7 +38,10 @@ static void generate_sine(const snd_pcm_channel_area_t *areas, unsigned char *samples[channels], *tmp; int steps[channels]; unsigned int chn, byte; - int ires; + union { + int i; + unsigned char c[4]; + } ires; unsigned int maxval = (1 << (snd_pcm_format_width(format) - 1)) - 1; int bps = snd_pcm_format_width(format) / 8; /* bytes per sample */ @@ -59,8 +62,8 @@ static void generate_sine(const snd_pcm_channel_area_t *areas, /* fill the channel areas */ while (count-- > 0) { res = sin(phase) * maxval; - ires = res; - tmp = (unsigned char *)(&ires); + ires.i = res; + tmp = ires.c; for (chn = 0; chn < channels; chn++) { for (byte = 0; byte < (unsigned int)bps; byte++) *(samples[chn] + byte) = tmp[byte]; @@ -868,7 +871,7 @@ int main(int argc, char *argv[]) if (verbose > 0) snd_pcm_dump(handle, output);
- samples = malloc((period_size * channels * snd_pcm_format_width(format)) / 8); + samples = malloc((period_size * channels * snd_pcm_format_physical_width(format)) / 8); if (samples == NULL) { printf("No enough memory\n"); exit(EXIT_FAILURE); @@ -881,8 +884,8 @@ int main(int argc, char *argv[]) } for (chn = 0; chn < channels; chn++) { areas[chn].addr = samples; - areas[chn].first = chn * snd_pcm_format_width(format); - areas[chn].step = channels * snd_pcm_format_width(format); + areas[chn].first = chn * snd_pcm_format_physical_width(format); + areas[chn].step = channels * snd_pcm_format_physical_width(format); }
err = transfer_methods[method].transfer_loop(handle, samples, areas);
On Thu, 10 Jul 2008, Takashi Iwai wrote:
At Thu, 10 Jul 2008 12:19:05 +0200 (CEST), Jaroslav Kysela wrote:
On Thu, 10 Jul 2008, Clemens Ladisch wrote:
Norbert van Bolhuis wrote:
as far as I know: sample format S24_LE is 24bit sample in 4 bytes sample format S24_3LE is 24bit sample in 3 bytes (why else have separate definitions), right ?
Yes.
In the ALSA-LIb example /test/pcm.c however (http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html) there is no diff between the 2 sample formats.
That example program uses snd_pcm_format_width() although it should have used snd_pcm_format_physical_width() when calculating memory buffer sizes.
I think that the problem is in wrong area->step calculation in alsa-lib, but I'm still investigating where the real culprit is. The snd_pcm_format_width() is used only for sample filling (which is OK).
I think Clemens is right. The program uses snd_pcm_format_width() wrongly. Also, it won't work properly with strict aliasing...
Yes, the patch looks good. I overlooked that the area initialization is directly in pcm.c code (I looked only to generate_sine(). I tested it and it produces good samples. I'm getting some underruns on my notebook with 24-bit formats (but it's probably different problem).
Jaroslav
----- Jaroslav Kysela perex@perex.cz Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc.
At Thu, 10 Jul 2008 12:41:39 +0200 (CEST), Jaroslav Kysela wrote:
On Thu, 10 Jul 2008, Takashi Iwai wrote:
At Thu, 10 Jul 2008 12:19:05 +0200 (CEST), Jaroslav Kysela wrote:
On Thu, 10 Jul 2008, Clemens Ladisch wrote:
Norbert van Bolhuis wrote:
as far as I know: sample format S24_LE is 24bit sample in 4 bytes sample format S24_3LE is 24bit sample in 3 bytes (why else have separate definitions), right ?
Yes.
In the ALSA-LIb example /test/pcm.c however (http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html) there is no diff between the 2 sample formats.
That example program uses snd_pcm_format_width() although it should have used snd_pcm_format_physical_width() when calculating memory buffer sizes.
I think that the problem is in wrong area->step calculation in alsa-lib, but I'm still investigating where the real culprit is. The snd_pcm_format_width() is used only for sample filling (which is OK).
I think Clemens is right. The program uses snd_pcm_format_width() wrongly. Also, it won't work properly with strict aliasing...
Yes, the patch looks good. I overlooked that the area initialization is directly in pcm.c code (I looked only to generate_sine(). I tested it and it produces good samples. I'm getting some underruns on my notebook with 24-bit formats (but it's probably different problem).
OK, committed now.
Takashi
participants (4)
-
Clemens Ladisch -
Jaroslav Kysela -
Norbert van Bolhuis -
Takashi Iwai