[FFmpeg-trac] #2938(undetermined:new): Incorrect start time and duration when transcoding audio-only (-vn) from A/V files.

[FFmpeg]

#2938: Incorrect start time and duration when transcoding audio-only (-vn) from
A/V files.
-------------------------------------+-------------------------------------
             Reporter:  rlabonte     |                    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 rlabonte):

 Replying to [comment:1 cehoyos]:
 > Replying to [ticket:2938 rlabonte]:
 > > Muxing to matroska or raw AAC results in a 0.00 start time, but the
 duration is still off by 40ms.
 >
 > Does this mean audio gets significantly longer (or shorter?) if you
 encode several times?

 I just realized I misinterpreted your question.  The short answer is the
 audio duration gets longer, but the offset remains the same.

 {{{
 % ffmpeg -i big_buck_bunny_480p_h264.mov -vn -c:a aac -strict -2
 offset1.mov && ffmpeg -i offset1.mov -vn -c:a aac -strict -2 offset2.mov
 && ffmpeg -i offset2.mov -vn -c:a aac -strict -2 offset3.mov
 }}}

 The FFprobe result for the final rendition:

 {{{
 % ffprobe offset3.mov -show_streams -show_format
 ffprobe version N-56052-g59b9ecc Copyright (c) 2007-2013 the FFmpeg
 developers
   built on Sep  5 2013 14:16:47 with gcc 4.4.3 (Ubuntu 4.4.3-4ubuntu5.1)
   configuration: --enable-nonfree --enable-gpl --enable-version3 --enable-
 libvpx --enable-libtheora --enable-libvorbis --enable-libfaac --enable-
 libfdk_aac --enable-libx264 --enable-libfreetype
   libavutil      52. 43.100 / 52. 43.100
   libavcodec     55. 31.101 / 55. 31.101
   libavformat    55. 16.101 / 55. 16.101
   libavdevice    55.  3.100 / 55.  3.100
   libavfilter     3. 83.102 /  3. 83.102
   libswscale      2.  5.100 /  2.  5.100
   libswresample   0. 17.103 /  0. 17.103
   libpostproc    52.  3.100 / 52.  3.100
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'offset3.mov':
   Metadata:
     major_brand     : qt
     minor_version   : 512
     compatible_brands: qt
     encoder         : Lavf55.16.101
   Duration: 00:09:56.54, start: 0.021333, bitrate: 129 kb/s
     Stream #0:0(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp,
 128 kb/s (default)
     Metadata:
       handler_name    : DataHandler
 [STREAM]
 index=0
 codec_name=aac
 codec_long_name=AAC (Advanced Audio Coding)
 profile=unknown
 codec_type=audio
 codec_time_base=1/48000
 codec_tag_string=mp4a
 codec_tag=0x6134706d
 sample_fmt=fltp
 sample_rate=48000
 channels=6
 bits_per_sample=0
 id=N/A
 r_frame_rate=0/0
 avg_frame_rate=0/0
 time_base=1/48000
 start_pts=-1024
 start_time=-0.021333
 duration_ts=28634112
 duration=596.544000
 bit_rate=128174
 nb_frames=27963
 nb_read_frames=N/A
 nb_read_packets=N/A
 DISPOSITION:default=1
 DISPOSITION:dub=0
 DISPOSITION:original=0
 DISPOSITION:comment=0
 DISPOSITION:lyrics=0
 DISPOSITION:karaoke=0
 DISPOSITION:forced=0
 DISPOSITION:hearing_impaired=0
 DISPOSITION:visual_impaired=0
 DISPOSITION:clean_effects=0
 DISPOSITION:attached_pic=0
 TAG:language=eng
 TAG:handler_name=DataHandler
 [/STREAM]
 [FORMAT]
 filename=offset3.mov
 nb_streams=1
 nb_programs=0
 format_name=mov,mp4,m4a,3gp,3g2,mj2
 format_long_name=QuickTime / MOV
 start_time=-0.021333
 duration=596.544000
 size=9670468
 bit_rate=129686
 probe_score=100
 TAG:major_brand=qt
 TAG:minor_version=512
 TAG:compatible_brands=qt
 TAG:encoder=Lavf55.16.101
 [/FORMAT]
 }}}

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2938#comment:3>
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