[FFmpeg-trac] #9941(undetermined:new): Remuxing mp4/dash file takes time that is exponential to the duration

[FFmpeg]

#9941: Remuxing mp4/dash file takes time that is exponential to the duration
-------------------------------------+-------------------------------------
             Reporter:  fireattack   |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:

 The input file is created by concatenating dash/mpd fragments downloaded
 from YouTube livestream.

 A sample file is provided at
 https://1drv.ms/u/s!Akq11jtCTJYwg7YXUeLvKe3OGoODEQ [414M, audio only]

 Keep in mind due to the nature of this issue, a long duration (this one is
 about 5h42m) file is needed to demonstrate it.

 How to reproduce:
 {{{
 % ffmpeg -i audio.ts -c copy output.m4a
 ffmpeg version 2022-08-29-git-f99d15cca0-full_build-www.gyan.dev Copyright
 (c) 2000-2022 the FFmpeg developers
   built with gcc 12.1.0 (Rev2, Built by MSYS2 project)
   configuration: --enable-gpl --enable-version3 --enable-static --disable-
 w32threads --disable-autodetect --enable-fontconfig --enable-iconv
 --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma
 --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt
 --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray
 --enable-libcaca --enable-sdl2 --enable-libdav1d --enable-libdavs2
 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1
 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2
 --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg
 --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r
 --enable-libfreetype --enable-libfribidi --enable-liblensfun --enable-
 libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-
 llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc
 --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libshaderc
 --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio
 --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-
 libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora
 --enable-libtwolame --enable-libvo-amrwbenc --enable-libilbc --enable-
 libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex
 --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite
 --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-
 chromaprint
   libavutil      57. 34.100 / 57. 34.100
   libavcodec     59. 42.103 / 59. 42.103
   libavformat    59. 30.100 / 59. 30.100
   libavdevice    59.  8.101 / 59.  8.101
   libavfilter     8. 46.103 /  8. 46.103
   libswscale      6.  8.104 /  6.  8.104
   libswresample   4.  9.100 /  4.  9.100
   libpostproc    56.  7.100 / 56.  7.100
 [mov,mp4,m4a,3gp,3g2,mj2 @ 00000000005d7600] Found duplicated MOOV Atom.
 Skipped it
     Last message repeated 10263 times
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'E:\test\1\audio.ts':
   Metadata:
     major_brand     : dash
     minor_version   : 0
     compatible_brands: iso6mp41
   Duration: 05:42:09.99, start: 0.000000, bitrate: 169 kb/s
   Stream #0:0[0x1](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz,
 stereo, fltp, 128 kb/s (default)
     Metadata:
       handler_name    : ISO Media file produced by Google Inc.
       vendor_id       : [0][0][0][0]
 Output #0, ipod, to 'D:\copy-only.m4a':
   Metadata:
     major_brand     : dash
     minor_version   : 0
     compatible_brands: iso6mp41
     encoder         : Lavf59.30.100
   Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo,
 fltp, 128 kb/s (default)
     Metadata:
       handler_name    : ISO Media file produced by Google Inc.
       vendor_id       : [0][0][0][0]
 Stream mapping:
   Stream #0:0 -> #0:0 (copy)
 Press [q] to stop, [?] for help
 size=  324238kB time=05:42:09.96 bitrate= 129.4kbits/s speed=21.4x
 video:0kB audio:320781kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 1.077679%
 }}}

 The above command took aboud 993s (16.3min) to finish, where about 34s was
 used on reading the input.
 So about 959s on remuxing the whole 5h42m.

 If adding -t 2:00:00, it only took 117s in total, or 83s for remuxing.
 If adding -t 1:00:00, it only took 49s in total, or 15s for remuxing.

 This looks like a bug to me, as I assume the time consumed should be
 roughly linear to the duration of the video.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9941>
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