[FFmpeg-trac] #615(undetermined:closed): ALSA buffer xrun
FFmpeg
trac at avcodec.org
Mon May 20 15:47:30 CEST 2013
#615: ALSA buffer xrun
-------------------------------------+-------------------------------------
Reporter: burek | Owner: michael
Type: defect | Status: closed
Priority: normal | Component:
Version: git-master | undetermined
Keywords: | Resolution:
Blocking: | needs_more_info
Analyzed by developer: 0 | Blocked By:
| Reproduced by developer: 0
-------------------------------------+-------------------------------------
Comment (by unknow):
i encounter the same problem.
it apear only when i record from alsa & x11grab
increasing ALSA_BUFFER_SIZE_MAX didn't seem to change anything
{{{
$ ffmpeg -f x11grab -r 25 -s 1152x864 -i 0:0+1,20 -f alsa -i default
-acodec libfaac -vcodec libx264 -preset ultrafast -y rec.mkv
}}}
or
{{{
$ ffmpeg -f x11grab -r 25 -s 1152x864 -i 0:0+1,20 -f alsa -i default
-acodec libfaac -vcodec libx264 -preset ultrafast -f null -y /dev/null
}}}
with 65535 or 6553500 i got xrun every ~30sec
the fun thing is changing audio option don't change anything but:
{{{
$ ffmpeg -f alsa -i default -f x11grab -r 10 -s 320x240 -i :0.0+1,20
-acodec libfaac -vcodec libx264 -preset ultrafast rec.mkv
}}}
works with a lot of
{{{
[libfaac @ 0xdf2a00] Queue input is backward in time
[matroska @ 0xdf1160] Non-monotonous DTS in output stream 0:1; previous:
281, current: 276; changing to 281. This may result in incorrect
timestamps in the output file.
}}}
but 0 xrun, sound and video is in sync
so
Replying to [comment:13 reimar]:
> Did you try capturing audio and video at the same time bug from
different FFmpeg processes?
> I would have guessed that due to the overhead of video processing FFmpeg
might not get data often enough from the audio device.
> Even if that is not the case, clocks and thus timestamps for audio and
video running apart might cause FFmpeg to read audio data not often
enough.
> For both cases creating a separate thread that can buffer far more data
than ALSA on its own (similar to what is done in libavformat/udp.c) should
help.
should be right
launching separatly
{{{
$ ffmpeg -f alsa -i default -acodec libfaac rec_va.mkv
$ ffmpeg -f x11grab -r 25 -s 1152x864 -i 0:0+1,20 -vcodec libx264 -preset
ultrafast rec_vo.mkv
}}}
got no xrun
--
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/615#comment:20>
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