[FFmpeg-devel] [RFC] libavdevice, audio output devices

Michael Niedermayer michaelni
Wed Nov 25 01:35:59 CET 2009

On Sun, Nov 22, 2009 at 08:44:30PM +0100, Ivo wrote:
> Hi,
> Recently, an issue came up on -cvslog and as per Michael's suggestion, I'm 
> posting it here, so it can be discussed.
> First some context:
> avformat.h:
> #define AVFMT_FLAG_NONBLOCK     0x0004 \
> 		///< Do not block when reading packets from input.
> alsa-audio-common.c:
>     if (ctx->flags & AVFMT_FLAG_NONBLOCK) {
>         flags = SND_PCM_NONBLOCK;
>     }
> oss_audio.c:
>     if (!is_output)
>         fcntl(audio_fd, F_SETFL, O_NONBLOCK);
> Basically, alsa blocks on input and output if AVFMT_FLAG_NONBLOCK is not set 
> and does not block on input and output if it is set. On the other hand, oss 
> always blocks on output, and never blocks on input. If you look at the 
> description in avformat.h, both are not functioning as is described.
> My proposal would be to extend AVFMT_FLAG_NONBLOCK to non-blocking behaviour 
> for output too and fix oss_audio. This leads to the greatest flexibility 
> for third-party applications using libavdevice.

if you can make muxers non blocking thats great, though i think this
will might be hard with more complex muxers


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
of college or go to community college in order to be able to afford
settlements. -- The RIAA
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