[FFmpeg-user] Recent ffmpeg gives warnings and buffer underflow during stream copy

Hans Carlson forbyta at inbox.com
Mon Jan 25 01:49:38 CET 2016

On Sun, 24 Jan 2016, Carl Eugen Hoyos wrote:

> How I can I reproduce this issue?

I get the 2 warning messages with all of the mpeg(mpeg2video/ac3) files 
I've tried so far.  All of my files are mpeg container with mpeg2 video 
and ac3 audio, some may have multiple ac3 audio streams and/or dvdsub 
subtitle streams.

The original source for these is either from DVDs dumped using mpv 
--stream-dump, or DVDs which have been re-muxed and/or re-encoded with 
ffmpeg or re-encoded from bluray mpegts/h264 using ffmpeg.

I *think* the buffer underflow errors are only seen on the files that were 
re-encoded from bluray .m2ts files.  The bluray source files would have 
been either mpegts(h264/dts) or mpegts(h264/ac3) and then scaled down from 
1920x1080 to 720x480 into mpeg(mpeg2video/ac3).

In most cases the re-encoding was done with some previous version of 
ffmpeg, BUT the example I gave in my initial message was created using the 
most recent ffmpeg (git master as of 01/23).   eg:

   $ ffmpeg-dev -i 'bluray/BDMV/STREAM/00101.m2ts' -codec:v mpeg2video -b:v 16384k -bufsize 4096k -maxrate 30000k -codec:a ac3 -b:a 448k -ar 48000 -vf scale=-1:720 -t 300 -f vob clip.mpg
   $ ffmpeg-dev -i clip.mpg -codec copy -f vob clip-copy-dev.mpg
   $ ffmpeg -i clip.mpg -codec copy -f vob clip-copy-2.8.5.mpg

Where "ffmpeg-dev" is git master (as of 01/23) and "ffmpeg" is 2.8.5.

To re-iterate what I said in my initial message, the copy done with git 
master gives the 2 warnings and buffer underflow errors and the copy done 
with 2.8.5 doesn't give any warnings/errors.

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