[Ffmpeg-devel] possible bug - ac3 transcoding
Sat Dec 16 21:39:45 CET 2006
I have XP Pro SP2 and I'm using a ffmpeg for windows binary that I downloaded
It is not the latest SVN but since I don't know how to build the latest SVN on
cygwin/mingw I have to post my results with SVN-7260.
This is the CLI that I'm using.
It was taken from BeHappy a windows frontend for many encoders, namely FFmpeg.
ffmpeg.exe -i gotk448.ac3 -y -acodec ac3 -ab 384 gotk384.ac3
And here is the log
FFmpeg version SVN-r7260, Copyright (c) 2000-2006 Fabrice Bellard, et al.
configuration: --enable-mp3lame --enable-libnut --enable-libogg
--enable-vorbis --enable-faad --enable-faac --enable-libgsm --enable-xvid
--enable-x264 --enable-mingw32 --enable-a52 --enable-dts --enable-pp
--enable-amr_nb --enable-amr_wb --enable-swscaler --enable-avisynth
--enable-gpl --enable-memalign-hack --cpu=i686 --extra-ldflags=-static
libavutil version: 49.1.0
libavcodec version: 51.26.0
libavformat version: 51.6.0
built on Dec 8 2006 17:40:35, gcc: 4.0.3
Input #0, ac3, from 'gotk448.ac3':
Duration: 01:34:06.9, start: 0.000000, bitrate: 448 kb/s
Stream #0.0: Audio: ac3, 48000 Hz, 5 channels, 448 kb/s
Output #0, ac3, to 'gotk384.ac3':
Stream #0.0: Audio: ac3, 48000 Hz, 5 channels, 384 kb/s
Stream #0.0 -> #0.0
Press [q] to stop encoding
size= 317640kB time=6776.3 bitrate= 384.0kbits/s
video:0kB audio:317640kB global headers:0kB muxing overhead 0.000000%
Note: I'm only using ffmpeg for audio transcoding.
I use a different encoder for the video part.
In the end I'll just mux them back with DVDLab Pro or Muxman Std..
In the above test the source movie is a original DVD PAL 25fps and it has a
total of 141175 frames.
I extracted the ac3 stream using DGMPGDec/DGIndex 1.4.8. which reports the ac3
stream as a 5.1 448kbps stream and it uses 308819KB of disc space.
After transcoding to 384kbit ac3 using the above CLI I get a file with 317640KB
thus making it _even_bigger_than_the_original_.
For me this doesn't make sense because if my math is right I should be getting
a file from ffmpeg with ~264703KB.
My math for the transcoded ac3: ((141175/25)*(384/8))/1024*1000=264703,125
And for the source ac3: ((141175/25)*(448/8))/1024*1000=308820,3125
Plus if I try to play the ffmpeg-transcoded file with either
foobar2000 0.9.4.1 or MediaPlayerClassic 126.96.36.199 my PC crashes and reboots.
I've tried several ffmpeg builds from that repository (celtic_druid's) as well
as from other repositories and I always get this problem.
FYI I am quite sure that this used to work with an older ffmpeg build from
19/04/2006, which already had the "ac3 low volume bug" fixed.
Unfortunately in one of my latest HDD housekeeping I accidentally erased that
build and I can't run a test with it just to make sure.
I raised this problem in the ffmpeg-users list and Mr. V?ctor Paesa told me
that he could reproduce my problem an he is on cygwin.
Here is one of his posts in that thread.
As you can see he sounds pretty much convinced that this is a bug.
If it is I need your help because I'd like to escalate it.
Merry Xmas to you all.
PS: yesterday I had already tried to post in this list but I got a mail from
the list saying that I was not a registered user and that my post would require
validation by a moderator or something similar.
So be nice with me :) if you get to see 2 posts very similar from the
same email address.
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