Re: Audio recording (using ossaudio)

[Yorick Hardy <yorickhardy%gmail.com@localhost>]

Dear Tetsuya,

On 2020-03-19, Tetsuya Isaki wrote:
> At Tue, 10 Mar 2020 20:49:55 +0200,
> Yorick Hardy wrote:
> >  ffmpeg4 -f oss -i /dev/audio -channels 1 -sample_rate 48000 /tmp/test.wav
> > 
> > is completely garbled and too short. The file also seems to be 2-channel,
> > so I think the recording settings are somehow not applied correctly.
> 
> I rarely use ffmpeg4 but according to ffmpeg4 documents,
> -channels/-sample_rate are for video and -ac/-ar are for audio?

If I used it correctly, it is for "-f oss" so for the input. Maybe it
should go before "-i", but if I recall correctly it does not make
a difference.

I think "-ac" is for the output format (ffmpeg performs appropriate
conversion).

>  % /usr/bin/time ffmpeg4 -f oss -t 0:05 -i /dev/audio -channels 1 test1.wav
>          5.04 real         0.02 user         0.04 sys
>  % file test1.wav
>  test1.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 48000 Hz
> 
>  % /usr/bin/time ffmpeg4 -f oss -t 0:05 -i /dev/audio -ac 1 test2.wav
>          5.04 real         0.04 user         0.02 sys
>  % file test2.wav
>  test2.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, mono 48000 Hz
> 
>  % /usr/bin/time audioplay test1.wav
>          2.54 real         0.00 user         0.00 sys
>  % /usr/bin/time audioplay test2.wav
>          2.54 real         0.00 user         0.00 sys
> 
> As you said, output file was too short.  However ffmpeg4 probably
> recorded specified period and created small file so that I think
> you need to look ffmpeg4 at first.

I did not figure out why the file is too short, but there is some
oss/ffmpeg interaction (maybe due to non-blocking reads?) which causes
this.

I created wip/ffmpeg4-nbsdaudio and nia improved it, and now recording
works fine:

 ffmpeg4 -f nbsdaudio -i /dev/audio /tmp/netbsd.wav

records as expected.

> Thanks,
> ---
> Tetsuya Isaki <isaki%pastel-flower.jp@localhost / isaki%NetBSD.org@localhost>

Thank you!

-- 
Kind regards,

Yorick Hardy