[FFmpeg-trac] #786(avformat:new): GXF file frame rate double what it should be for some files.

[FFmpeg]

#786: GXF file frame rate double what it should be for some files.
----------------------------------+--------------------------------------
             Reporter:  ryaowe    |                     Type:  defect
               Status:  new       |                 Priority:  normal
            Component:  avformat  |                  Version:  git-master
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
----------------------------------+--------------------------------------
 * Trying to accomplish: Transcode a GXF (mpeg2 video, pcm16le audio) to
 any other format
  * Problem encountered: Transcoded video plays back at twice the rate it
 should.
  * Command line: ffmpeg -i fyi.gxf -t 30 -acodec libfaac fyi.mp4
  * ffmpeg -v 9 -loglevel 99 -i fyi.gxf:
 {{{
 ffmpeg version N-35872-g6d8e6fe, Copyright (c) 2000-2011 the FFmpeg
 developers
   built on Dec 16 2011 16:49:56 with gcc 4.2.1 (Apple Inc. build 5666)
 (dot 3)
   configuration: --enable-shared --disable-static --disable-doc --enable-
 memalign-hack --enable-nonfree --enable-gpl --enable-libfaac --cc=gcc-4.2
 --prefix=/Users/ryanowen/src/protoven/uplynk/dependencies/encoder_Darwin_64
 --enable-pic --extra-ldflags=-headerpad_max_install_names --enable-debug=3
   libavutil    51. 32. 0 / 51. 32. 0
   libavcodec   53. 46. 0 / 53. 46. 0
   libavformat  53. 26. 0 / 53. 26. 0
   libavdevice  53.  4. 0 / 53.  4. 0
   libavfilter   2. 53. 0 /  2. 53. 0
   libswscale    2.  1. 0 /  2.  1. 0
   libpostproc  51.  2. 0 / 51.  2. 0
 [gxf @ 0x7fa48303d820] Format gxf probed with size=2048 and score=100
 [mpeg2video @ 0x7fa48304e620] err{or,}_recognition separate: 1; 1
 [mpeg2video @ 0x7fa48304e620] err{or,}_recognition combined: 1; 10001
 [pcm_s16le @ 0x7fa48303fc20] err{or,}_recognition separate: 1; 1
 [pcm_s16le @ 0x7fa48303fc20] err{or,}_recognition combined: 1; 10001
 [pcm_s16le @ 0x7fa483040220] err{or,}_recognition separate: 1; 1
 [pcm_s16le @ 0x7fa483040220] err{or,}_recognition combined: 1; 10001
 [mpeg2video @ 0x7fa48304e620] Unsupported bit depth: 0
 [gxf @ 0x7fa48303d820] All info found

 Seems stream 0 codec frame rate differs from container frame rate: 119.88
 (120000/1001) -> 59.94 (120000/2002)
 Input #0, gxf, from 'fyi.gxf':
   Metadata:
     gxf_timecode    : 01:00:48;38
     gxf_timecode_at_mark_in: 01:00:48;38
     gxf_timecode_at_mark_out: 01:11:38;50
   Duration: 00:05:25.09, start: 0.000000, bitrate: 85613 kb/s
     Stream #0:0, 41, 1001/120000: Video: mpeg2video (4:2:2), yuv422p,
 1280x720 [SAR 1:1 DAR 16:9], 1001/120000, 50000 kb/s, 119.88 fps, 59.94
 tbr, 119.88 tbn, 119.88 tbc
     Stream #0:1, 2, 1001/120000: Audio: pcm_s16le, 48000 Hz, 1 channels,
 s16, 768 kb/s
     Stream #0:2, 2, 1001/120000: Audio: pcm_s16le, 48000 Hz, 1 channels,
 s16, 768 kb/s
     Stream #0:3, 0, 1001/120000: Data: none
 At least one output file must be specified
 }}}
 Some GXF files end up with a frame rate for the video track that is twice
 what it should be.  In my case, the time base should be 1001 / 60000, but
 was 1001 / 120000.

 The problem seems to coincide with files that have a fields_per_frame
 value of 1 instead of 2.  The following patch solved the problem for me,
 and allows me to dencode all of my GXF files correctly (both those that
 did and did not work correctly prior to the fix).

 {{{
 diff --git a/libavformat/gxf.c b/libavformat/gxf.c
 index 95a8142..1d9f059 100644
 --- a/libavformat/gxf.c
 +++ b/libavformat/gxf.c
 @@ -351,7 +351,7 @@ static int gxf_header(AVFormatContext *s,
 AVFormatParameters *ap) {
          st = s->streams[idx];
          if (!main_timebase.num || !main_timebase.den) {
              main_timebase.num = si->frames_per_second.den;
 -            main_timebase.den = si->frames_per_second.num * 2;
 +            main_timebase.den = si->frames_per_second.num *
 (si->fields_per_frame ? si->fields_per_frame : 2);
          }
          st->start_time = si->first_field;
          if (si->first_field != AV_NOPTS_VALUE && si->last_field !=
 AV_NOPTS_VALUE)
 }}}

 I'll upload a test file to upload.ffmpeg.org, called double_framerate.gxf

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/786>
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