[Ffmpeg-devel] [BUG] -vframes with x264 encoding and b frames

[Baptiste Coudurier]

Hi

I just spotted a bug when using -vframes with h264 encoding (x264):

ffmpeg -vframes 100 -i file.mpg -vcodec h264 -bf 2 test.h264


FFmpeg version SVN-r6848, Copyright (c) 2000-2006 Fabrice Bellard, et al.
  configuration:  --enable-gpl --enable-faac --enable-dts --enable-a52
--enable-x264 --enable-faad --enable-static --enable-mp3lame
--enable-pthreads --enable-xvid --enable-pp --enable-amr_nb --enable-amr_wb
  libavutil version: 49.0.2
  libavcodec version: 51.23.0
  libavformat version: 50.6.0
  built on Oct 31 2006 11:56:20, gcc: 4.1.2 20061028 (prerelease)
(Debian 4.1.1-19)

Seems that stream 0 comes from film source: 25.00 (25025/1001) -> 25.00
(25/1)
Input #0, mpeg, from 'file.mpg':
  Duration: 00:00:24.1, start: 0.220000, bitrate: 11959 kb/s
  Stream #0.0[0x1e0]: Video: mpeg2video, yuv422p, 720x608, 11386 kb/s,
25.00 fps(r)
  Stream #0.1[0x1c0]: Audio: mp2, 48000 Hz, stereo, 384 kb/s
File 'test.h264' already exists. Overwrite ? [y/N] y
Output #0, h264, to 'test.h264':
  Stream #0.0: Video: h264, yuv420p, 720x608, q=2-31, 200 kb/s, 25.00 fps(c)
Stream mapping:
  Stream #0.0 -> #0.0
[h264 @ 0x85dd338]using SAR=1/1
[h264 @ 0x85dd338]using cpu capabilities MMX MMXEXT SSE SSE2
Press [q] to stop encoding
frame=  100 q=31.0 Lsize=     292kB time=3.9 bitrate= 616.3kbits/s
video:292kB audio:0kB global headers:0kB muxing overhead 0.000000%
[h264 @ 0x85dd338]slice I:9     Avg QP:31.00  size:  7526
[h264 @ 0x85dd338]slice P:33    Avg QP:31.00  size:  4165
[h264 @ 0x85dd338]slice B:56    Avg QP:33.00  size:  1659
[h264 @ 0x85dd338]mb I  I16..4: 80.7%  0.0% 19.3%
[h264 @ 0x85dd338]mb P  I16..4: 22.1%  0.0%  0.0%  P16..4: 14.4%  0.0%
0.0%  0.0%  0.0%    skip:63.5%
[h264 @ 0x85dd338]mb B  I16..4:  5.5%  0.0%  0.0%  B16..8: 15.4%  0.0%
0.0%  direct: 0.9%  skip:78.2%
[h264 @ 0x85dd338]final ratefactor: 38.75
[h264 @ 0x85dd338]SSIM Mean Y:0.9726804
[h264 @ 0x85dd338]kb/s:608.3

x264 clearly says total frames number is 98.
Increasing number to 101 gives 99, 102 gives 100, 103 gives 101.

Now when not using bf 2:
ffmpeg -vframes 100 -i file.mpg -vcodec h264 test.h264

[h264 @ 0x85dd338]using SAR=1/1
[h264 @ 0x85dd338]using cpu capabilities MMX MMXEXT SSE SSE2
Press [q] to stop encoding
frame=  100 q=31.0 Lsize=     321kB time=4.0 bitrate= 657.9kbits/s
video:321kB audio:0kB global headers:0kB muxing overhead 0.000000%
[h264 @ 0x85dd338]slice I:9     Avg QP:29.33  size:  8460
[h264 @ 0x85dd338]slice P:91    Avg QP:31.00  size:  2770
[h264 @ 0x85dd338]mb I  I16..4: 78.9%  0.0% 21.1%
[h264 @ 0x85dd338]mb P  I16..4: 12.8%  0.0%  0.0%  P16..4: 16.0%  0.0%
0.0%  0.0%  0.0%    skip:71.2%
[h264 @ 0x85dd338]final ratefactor: 38.67
[h264 @ 0x85dd338]SSIM Mean Y:0.9752094
[h264 @ 0x85dd338]kb/s:656.4

Final count is correctly 100 frames.

The bug does not appear when using lavc mpeg4 encoder with b frames.

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
SMARTJOG S.A.                                    http://www.smartjog.com
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