[Ffmpeg-devel] [bugs] grabbing v4l2 -> buffer underflow ; packet too large ; pcm_s16le vs mp2

[Luca Abeni]

Hi,

On Thu, 2006-02-23 at 18:10 +0000, Dieter wrote:
[...]
> Tried outputting mpeg instead, and got a bunch of complaints
> about buffer underflow and packet too large:
> 
> FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
>   configuration:  --prefix=/app --disable-bktr --disable-ffserver --disable-ffplay --disable-audio-beos --disable-v4l --enabl
> e-memalign-hack --enable-gpl --disable-network --disable-strip --enable-a52 --extra-cflags=-DHAVE_LRINTF -mcpu=athlon-4 -msse
> 2 -msse3 
>   libavutil version: 49.0.0
>   libavcodec version: 51.7.0
>   libavformat version: 50.3.0
>   built on Feb 23 2006 13:53:26, gcc: 3.3.5 20050117 (prerelease) (SUSE Linux)
> [video4linux2 @ 0x82d1518][4]Capabilities: 5010015
> Device Init(720 480 842093913)
> Device Init(720 480 1345466932)
> Device Init(720 480 1448695129)
> Frame Format: 1448695129
> Number of buffers: 27
> Input #0, video4linux2, from '':
>   Duration: N/A, bitrate: N/A
>   Stream #0.0, 1/1000000, 29.97 fps(r): Video: rawvideo, yuv422, 640x480, 1001/30000, 147308 kb/s
> Input #1, audio_device, from '':
>   Duration: N/A, bitrate: N/A
>   Stream #1.0, 1/1000000: Audio: pcm_s16le, 48000 Hz, stereo, 1536 kb/s
> Output #0, mpeg, to '/video/2006_02_23_chan10ntsc_t1_1min_test_audioargs_2_ffmpeg.mpeg':
>   Stream #0.0, 1/90000, 29.97 fps(c): Video: mpeg1video, yuv420p, 720x480, 1001/30000, q=2-31, 200 kb/s
I think the problem is that you are trying to encode MPEG1 video with
size 720x480 at 200kbps. This cannot work ;-) Try to add "-b 5000", and
maybe some buffer underflow will disappear.
>   Stream #0.1, 1/90000: Audio: pcm_s16le, 48000 Hz, stereo, 1536 kb/s
PCM audio in an MPEG file? Is this valid? (Just asking, because I do not
know...)
BTW, how does the result look like? Ok, it will be _very_ blocky, but I
am insterested in knowing if you can see any artifacts caused by the
v4l2 input.

[...]
> So we have
> 
> 	DV encoder VLC bit accounting  [ fixed but probably not checked in yet ]
> 	yuv420p vs yuv411p
Don't know about this problem... Is it a DV thing?
> 	pcm_s16le vs mp2
I do not know if the mpeg muxer / demuxer in libavformat can understand
PCM in mpeg (as I said, I do not even know if it is a valid
combination). Try to use mp2 audio... Or just use a different container
(maybe avi can be ok?).
> 	buffer underflow / packet too large
This is probably due to a too low bitrate used for encoding video. Try
to encode at a higher bitrate.

				Luca

 
 
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