[FFmpeg-trac] #3859(undetermined:new): mp4: start_time never zero

[FFmpeg]

#3859: mp4: start_time never zero
-------------------------------------+-------------------------------------
             Reporter:  blacktrash   |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  git-master   |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------

Comment (by blacktrash):

 It's a problem with mp4 audio or aac, the duration is too long - I guess
 ffmpeg tries to accomodate that by setting a negative start_time when
 transcoding and muxing. If I encode the audio separately and mux it in
 with -c:a copy start_time is 0, but that only shifts the issue because it
 is still longer than the video (or the orginal audio track for that
 matter). The values vary depending on the aac library (or native) used,
 and sample rate.
 {{{
 $ ffmpeg -v quiet -i BigBuckBunny_640x360.m4v -vn -c:a copy copy.m4a
 $ ffmpeg -v quiet -i BigBuckBunny_640x360.m4v -vn -strict -2 -c:a aac -b:a
 64k native.m4a
 $ ffmpeg -v quiet -i BigBuckBunny_640x360.m4v -vn -c:a libfdk_aac
 -profile:a aac_he -b:a 64k fdk.m4a
 $ ffmpeg -v quiet -i BigBuckBunny_640x360.m4v -vn -c:a libfaac -b:a 64k
 faac.m4a
 $ ffprobe -v quiet -show_entries stream=start_time,duration copy.m4a
 [STREAM]
 start_time=0.000000
 duration=596.474195
 [/STREAM]
 $ ffprobe -v quiet -show_entries stream=start_time,duration native.m4a
 [STREAM]
 start_time=-0.023220
 duration=596.497415
 [/STREAM]
 $ ffprobe -v quiet -show_entries stream=start_time,duration faac.m4a
 [STREAM]
 start_time=-0.023220
 duration=596.497415
 [/STREAM]
 $ ffprobe -v quiet -show_entries stream=start_time,duration fdk.m4a
 [STREAM]
 start_time=-0.114694
 duration=596.588889
 [/STREAM]
 $ ffprobe -show_entries stream=start_time,duration
 BigBuckBunny_640x360.m4v
 ffprobe version N-66357-g28dce3c Copyright (c) 2007-2014 the FFmpeg
 developers
   built on Sep 21 2014 11:24:50 with Apple LLVM version 6.0
 (clang-600.0.51) (based on LLVM 3.5svn)
   configuration: --enable-gpl --enable-version3 --enable-nonfree
 --disable-ffserver --enable-shared --enable-libfdk-aac --enable-libx265
 --enable-libx264 --enable-libxvid --enable-libfaac --enable-libmp3lame
 --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libvidstab
 --extra-cflags=-I/sw/include --extra-libs=-L/sw/lib
   libavutil      54.  7.100 / 54.  7.100
   libavcodec     56.  1.101 / 56.  1.101
   libavformat    56.  4.102 / 56.  4.102
   libavdevice    56.  0.100 / 56.  0.100
   libavfilter     5.  1.101 /  5.  1.101
   libswscale      3.  0.100 /  3.  0.100
   libswresample   1.  1.100 /  1.  1.100
   libpostproc    53.  0.100 / 53.  0.100
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'BigBuckBunny_640x360.m4v':
   Metadata:
     major_brand     : M4V
     minor_version   : 1
     compatible_brands: M4V M4A mp42isom
     creation_time   : 2008-06-03 05:23:28
     copyright       : © 2008 Blender Foundation | www.bigbuckbunny.org
     title           : Big Buck Bunny
     artist          : Peach Open Movie Team
     composer        : Sacha Goedegebure / Ton Roosendaal
     date            : 2008
   Duration: 00:09:56.46, start: 0.000000, bitrate: 1626 kb/s
     Stream #0:0(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo,
 fltp, 127 kb/s (default)
     Metadata:
       creation_time   : 2008-06-03 05:23:28
       handler_name    : Apple Sound Media Handler
     Stream #0:1(eng): Video: h264 (Constrained Baseline) (avc1 /
 0x31637661), yuv420p(tv, smpte170m), 640x360, 1495 kb/s, 24 fps, 24 tbr,
 2400 tbn, 4800 tbc (default)
     Metadata:
       creation_time   : 2008-06-03 05:23:28
       handler_name    : Apple Video Media Handler
 [STREAM]
 start_time=0.000000
 duration=596.474195
 [/STREAM]
 [STREAM]
 start_time=0.000000
 duration=596.491667
 [/STREAM]
 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/3859#comment:13>
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