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Old 23rd July 2012, 21:54   #1  |  Link
ramprasad85
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Join Date: Oct 2008
Location: Chennai India
Posts: 31
x264 seems to changes the video duration of Variable Frame Rate video

I downloaded the latest x264.exe (core:125 r2208 d9d2288)

Encoded a VFR video of duration 143.733 sec, the duration of the encoded video is 137.501 sec

Here is the source video: http://dl.dropbox.com/u/55917837/Lon...12__Intro.webm

Here is the encoded video: http://dl.dropbox.com/u/55917837/olympics.mp4

When I try to compare the videos side-by-side, this difference in duration makes the videos out of sync, make it difficult to compare.

Here are the steps to reproduce
Code:
C:\>ffprobe -show_format -v quiet -print_format json London_Summer_Olympics_2012__Intro.webm
{
  "format": {
    "filename": "London_Summer_Olympics_2012__Intro.webm",
    "nb_streams": 2,
    "format_name": "matroska,webm",
    "format_long_name": "Matroska/WebM file format",
    "start_time": "0.000",
    "duration": "143.733",
    "size": "22478255",
    "bit_rate": "1251111"
  }
}

C:\>x264 -o olympics.mp4 London_Summer_Olympics_2012__Intro.webm 
ffms [info]: 640x480p 1:1 @ 4484/143 fps (vfr)
x264 [info]: using SAR=1/1
x264 [info]: using cpu capabilities: MMX2 SSE2Fast FastShuffle SSEMisalign LZCNT

x264 [info]: profile High, level 3.0
x264 [info]: frame I:113   Avg QP:19.21  size: 20566
x264 [info]: frame P:2745  Avg QP:26.45  size:  4284
x264 [info]: frame B:1454  Avg QP:29.79  size:   979
x264 [info]: consecutive B-frames: 48.4% 16.8%  8.8% 25.9%
x264 [info]: mb I  I16..4: 29.8% 54.7% 15.6%
x264 [info]: mb P  I16..4:  2.0%  5.6%  1.3%  P16..4: 34.7%  9.6%  4.1%  0.0%  0.0%    skip:42.7%
x264 [info]: mb B  I16..4:  0.2%  0.4%  0.1%  B16..8: 31.6%  2.0%  0.3%  direct: 0.8%  skip:64.6%  L0:46.3% L1:47.5% BI: 6.2%
x264 [info]: 8x8 transform intra:60.0% inter:67.7%
x264 [info]: coded y,uvDC,uvAC intra: 58.2% 55.8% 24.8% inter: 13.4% 9.7% 0.6%
x264 [info]: i16 v,h,dc,p: 37% 40% 11% 13%
x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 17% 27% 18%  4%  6%  6%  7%  6%  8%
x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 17% 34% 18%  4%  6%  6%  6%  4%  5%
x264 [info]: i8c dc,h,v,p: 50% 29% 15%  6%
x264 [info]: Weighted P-Frames: Y:1.4% UV:0.5%
x264 [info]: ref P L0: 70.9% 18.5%  7.6%  2.8%  0.1%
x264 [info]: ref B L0: 92.8%  6.4%  0.8%
x264 [info]: ref B L1: 97.0%  3.0%
x264 [info]: kb/s:902.23

encoded 4312 frames, 153.00 fps, 902.28 kb/s


C:\>ffprobe -show_format -v quiet -print_format json olympics.mp4
{
  "format": {
    "filename": "olympics.mp4",
    "nb_streams": 1,
    "format_name": "mov,mp4,m4a,3gp,3g2,mj2",
    "format_long_name": "QuickTime/MPEG-4/Motion JPEG 2000 format",
    "start_time": "0.000",
    "duration": "137.501",
    "size": "15582670",
    "bit_rate": "906621",
    "tags": {
        "major_brand": "avc1",
        "minor_version": "0",
        "compatible_brands": "isomavc1",
        "creation_time": "2012-07-23 19:32:00"
    }
  }
}
Thanks and Regards
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Old 23rd July 2012, 22:56   #2  |  Link
MasterNobody
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Join Date: Jul 2007
Posts: 546
This webm-file contains wrong timing information (or at least it parsed incorrectly by mkvtoolnix and ffms: timecode file) according to which first 4312-frames have duration of 2:17.5 but in reality it is constant 30 fps video and this 4312-frames should have duration of 2:23.73. I guess this problem can have something todo with not-displaying frames of VP8 (which imho shouldn't present [ignored] in timecode file [parsing]).

Edit: that is ffms bug not lavf (because with --demuxer lavf it should result with correct duration)

Last edited by MasterNobody; 23rd July 2012 at 23:40.
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Old 24th July 2012, 03:36   #3  |  Link
Plorkyeran
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Join Date: Mar 2008
Posts: 26
I've fixed one bug related to this in FFMS2 r701, but the file seems to have a few issues. Your ffprobe output isn't even reporting the file size correctly (it's 28 MB, not 22). mkvmerge complains about corruption when reading the file; Opera, Chrome and mplayer2 can only play the first ~30 seconds, while MPC-HC agrees with ffms about the duration being 1:40.
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