[FFmpeg-devel] rawvideo/avi bug?

[Martin Gentry]

(Apologies if this eventually goes through twice, I tried posting yesterday and didn't ever receive the email from the list -- yes, my settings are such that I should receive my own posts.)

I'm assuming ffmpeg-devel is appropriate for this if I'm going to be attempting to submit a patch (if needed).

There appears to be a bug with raw video AVI support.

I discovered that when going from this rawvideo avi to rawvideo avi the image gets flipped vertically (maybe excluding a -vcodec copy?).  The original source video I'm using plays fine in Windows Media Player.  After one pass through FFmpeg to convert to a rawvideo bgr24 avi the video plays back upside down.  Passing that upside down video through FFmpeg again turns it right-side up again.  (See full command lines and output below.)

After a brief period of debugging and looking at FFmpeg's source code for the first time the issue seems to be the handling of the height in the bitmap header portion of the input.  The source video contains a positive height and so the pixel data is arranged bottom to top.  The code in rawdec.c just always flips video if the codec_tag is 0, bits_per_sample is non-zero and linesize[2] is 0, with a positive height value this is correct.  However along the way to being re-encoded as bgr24 raw video the frame data ends up right side up and thus the height in the bitmap header in the output avi should be negative.  I temporarily just naively modified avienc.c to just always write a negative height and the output then plays back correctly after the first time through FFmpeg but the file cannot then be used as input into FFmpeg.  Given negative heights render the input invalid from the code's point of view, the rawdec.c code is fine since it'll only get that far if the pixel data actually does need to be flipped.

Anyway, at this point I don't have enough familiarity with the code to just dive into the correct place to fix this (assuming people even agree that it's a bug).

I'm more than willing to submit a patch assuming I can figure out what to fix, but if anyone has some way to point me in the correct direction that would certainly save me some time.  In particular, is it proper to use AVCodecContext.coded_height for all this and set it appropriately (pos or neg)?  Is there already something that should be taking care of this that I'm just not aware of?  Am I just plain wrong about what the problem is?

Thanks,
-martin


------
Starting with input.avi that plays correctly in WMP ...

$ ffmpeg -i input.avi -t 30 -acodec copy -vcodec rawvideo -pix_fmt bgr24 -vhook ./libenscramblevhook.so bgr24-1.avi
FFmpeg version SVN-r9791, Copyright (c) 2000-2007 Fabrice Bellard, et al.
  configuration: --disable-shared --enable-static --enable-libogg --enable-libvorbis
  libavutil version: 49.4.1
  libavcodec version: 51.40.4
  libavformat version: 51.12.1
  built on Jul 24 2007 14:34:51, gcc: 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)
Input #0, avi, from ' input.avi':
  Duration: 00:01:59.1, start: 0.000000, bitrate: 48237 kb/s
  Stream #0.0: Video: rawvideo, rgb555, 480x260, 23.98 fps(r)
  Stream #0.1: Audio: pcm_s16le, 22050 Hz, mono, 352 kb/s
Output #0, avi, to ' bgr24-1.avi':
  Stream #0.0: Video: rawvideo, bgr24, 480x260, q=2-31, 200 kb/s, 23.98 fps(c)
  Stream #0.1: Audio: pcm_s16le, 22050 Hz, mono, 352 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Press [q] to stop encoding
frame=  720 fps= 30 q=0.0 Lsize=  264822kB time=30.0 bitrate=72307.2kbits/s   
video:263250kB audio:1292kB global headers:0kB muxing overhead 0.105631%

Resulting bgr24-1.avi plays back upside down in WMP.

$ ffmpeg -i bgr24-1.avi -t 30 -acodec copy -vcodec rawvideo -pix_fmt bgr24 -vhook ./libenscramblevhook.so bgr24-2.avi
FFmpeg version SVN-r9791, Copyright (c) 2000-2007 Fabrice Bellard, et al.
  configuration: --disable-shared --enable-static --enable-libogg --enable-libvorbis
  libavutil version: 49.4.1
  libavcodec version: 51.40.4
  libavformat version: 51.12.1
  built on Jul 24 2007 14:34:51, gcc: 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)
Input #0, avi, from ' bgr24-1.avi':
  Duration: 00:00:30.0, start: 0.000000, bitrate: 72242 kb/s
  Stream #0.0: Video: rawvideo, bgr24, 480x260, 23.98 fps(r)
  Stream #0.1: Audio: pcm_s16le, 22050 Hz, mono, 352 kb/s
Output #0, avi, to ' bgr24-2.avi':
  Stream #0.0: Video: rawvideo, bgr24, 480x260, q=2-31, 200 kb/s, 23.98 fps(c)
  Stream #0.1: Audio: pcm_s16le, 22050 Hz, mono, 352 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Press [q] to stop encoding
frame=  720 fps= 28 q=0.0 Lsize=  264822kB time=30.0 bitrate=72307.2kbits/s   
video:263250kB audio:1292kB global headers:0kB muxing overhead 0.105631%

Resulting bgr24-2.avi plays back correctly in WMP.