[Ffmpeg-devel] Question about FAQ 1.3

Luca Abeni lucabe72
Sun Dec 11 13:03:52 CET 2005

Hi Vidar,

On Sat, 2005-12-10 at 19:50 +0100, Vidar Madsen wrote:
> I'm not sure if this the problem the FAQ talks about, since it's not
> exactly a synch problem, but I'm having a hard time grabbing with
> ffmpeg.
> I don't think it's ffmpeg's fault, though. Not directly, anyhow. My
> problem seems to be that my audio driver blocks while filling some
> buffers or something like that, thereby making ffmpeg miss several
> video frames while waiting for the audio read.
I've seen a similar problem: basically, ffmpeg opens the audio device in
non-blocking mode, but almos all the old OSS drivers do not support
non-blocking input... The only driver that works ok is the ES1371 driver
(try an old ES1371 based card, and it will work).

> My solution (or rather workaround) has been to use a threaded grabber,
> such as mencoder or mp1e. Then everything works as expected.
Well, in my experience there is a simpler solution: use recent ALSA
drivers with OSS emulation. My experience is that they work very well in
non-blocking mode, and I am able to capture good audio and video even
with the non-threaded "ffmpeg" program.

> So, if this is the problem the FAQ talks about, perhaps some kind of
> elaboration is in order? If not, move along, nothing to see here.
> (Unless you want to add threaded capture to ffmpeg.) ;)
If this really is the problem described by the FAQ, the FAQ has to be
updated (a better description of the problem would be useful, and
something like "use recent ALSA" could be added).


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