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• Why can't I get a manually modified MPEG-4 extended box (chunk) size to work ?

  15 avril 2019, par Moshe Rubin

  Overview

  As part of a project to write an MPEG-4 (MP4) file parser, I need to understand how an extended box (or chunk) size is processed within an MP4 file. When I tried to manually simulate an MP4 file with an extended box size, media players report that the file is invalid.

  Technical Information

  Paraphrasing the MPEG-4 specification :

  An MP4 file is formed as a series of objects called ’boxes’. All data is contained in boxes, there is no other data within the file.

  Here is a screen capture of Section 4.2 : Object Structure, which describes the box header and its size and type fields :

  

  

  Most MP4 box headers contain two fields : a 32-bit compact box size and a 32-bit box type. The compact box size supports a box’s data up to 4 GB. Occasionally an MP4 box may have more data than that (e.g., a large video file). In this case, the compact box size is set to 1, and eight (8) octets are added immediately following the box type. This 64-bit number is known as the ’extended box size’, and supports a box’s size up to 2^64.

  To understand the extended box size better, I took a simple MP4 file and wanted to modify the moov/trak/mdia box to use the extended box size, rather than the compact size.

  Here is what the MP4 file looks like before modifying it. The three box headers are highlighted in RED :

  

  My plan was as follows :

  1. Modify the moov/trak/mdia box
     • In the moov/trak/mdia, insert eight (8) octets immediately following the box type (’mdia’). This will eventually be our extended box size.
     • Copy the compact box size to the newly-inserted extended box size, adding 8 to the size to compensate for the newly inserted octets. The size is inserted in big-endian order.
     • Set the compact size to 1.
  2. Modify the moov/trak box
     • Add 8 to the existing compact box size (to compensate for the eight octets added to mdia).
  3. Modify the moov box
     • Add 8 to the existing compact box size (again, to compensate for the eight octets in mdia)

  Here’s what the MP4 file looks like now, with the modified octets are in RED :

  

  What have we done ?

  We have told the MP4 parser/player to take the moov/trak/mdia box size from the extended field rather than the compact size field, and have increased all parent boxes by eight (8) to compensate for the newly-inserted extended box size in the mdia box.

  What’s the problem ?

  When I attempt to play the modified MP4 file I receive error messages from different media players :

  

  

  Why do the media players see the modified file as invalid MP4 ?

  • Did I need to alter any other fields ?
  • Does the extended box size have to be greater than 2^32 ?
  • Can it be that only specific box types support extended box size (e.g., Media Data) ?

• FFMPEG fails with only two input frames

  3 mars 2019, par JeffThompson

  I’d like to use ffmpeg’s great frame interpolation to blend two images. I get great results when testing with about a dozen frames, but when only using two it finishes immediately and I get a video file that can’t be opened.

  My command :

  ffmpeg -y -r 24 -pattern_type glob -i "TestFrames/*[0-1].png" -pix_fmt yuv420p -filter:v "minterpolate='mi_mode=mci:mc_mode=aobmc:me_mode=bidir:vsbmc=1:fps=1024'" -vsync 2 8.mp4

  Output from ffmpeg :

  ffmpeg version 4.1.1 Copyright (c) 2000-2019 the FFmpeg developers
  
    built with Apple LLVM version 10.0.0 (clang-1000.11.45.5)
  
    configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1.1 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home/include/darwin' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-videotoolbox --disable-libjack --disable-indev=jack --enable-libaom --enable-libsoxr
  
    libavutil      56. 22.100 / 56. 22.100
  
    libavcodec     58. 35.100 / 58. 35.100
  
    libavformat    58. 20.100 / 58. 20.100
  
    libavdevice    58.  5.100 / 58.  5.100
  
    libavfilter     7. 40.101 /  7. 40.101
  
    libavresample   4.  0.  0 /  4.  0.  0
  
    libswscale      5.  3.100 /  5.  3.100
  
    libswresample   3.  3.100 /  3.  3.100
  
    libpostproc    55.  3.100 / 55.  3.100
  
  Input #0, image2, from 'TestFrames/*.png':
  
    Duration: 00:00:00.08, start: 0.000000, bitrate: N/A
  
      Stream #0:0: Video: png, rgba(pc), 1080x1080, 25 tbr, 25 tbn, 25 tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  [libx264 @ 0x7fa5c2813200] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
  
  [libx264 @ 0x7fa5c2813200] profile High, level 6.1
  
  [libx264 @ 0x7fa5c2813200] 264 - core 155 r2917 0a84d98 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to '8.mp4':
  
    Metadata:
  
      encoder         : Lavf58.20.100
  
      Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 1080x1080, q=-1--1, 1024 fps, 16384 tbn, 1024 tbc
  
      Metadata:
  
        encoder         : Lavc58.35.100 libx264
  
      Side data:
  
        cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
  
  frame=    0 fps=0.0 q=0.0 Lsize=       0kB time=00:00:00.00 bitrate=N/A speed=   0x    
  
  video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

  (Why fps=1024 ? I wanted to generate a a bunch of frames between the two images, so I plan to later separate the resulting video into separate images.)

• Evolution #4300 (Nouveau) : Rendre facultatif les plugins-dist

  1er mars 2019, par Franck D

  Hello :-)
  Le commit de toutati https://zone.spip.net/trac/spip-zone/changeset/114194/spip-zone m’a fait repenser à ce vieux sujet (2009) https://blog.spip.net/SPIP-Core-tout-change-rien-ne-change.html
  Jluc avait fait un sujet à ce propos https://contrib.spip.net/plugins-dist-indispensables-ou-non
  Je me doute que cela représente un boulot de malade... mais ne faudrait’il pas dire au moins dans la F.A.Q. https://www.spip.net/fr_rubrique170.html les plugins-dist qui sont encore obligatoire ?

  J’ai fait le choix de "evolution" et non de "documentation" concernant le ticket, car sans ticket personne n’y pense :-D
  Pour spip 3.3, c’est sans doute un peu tard, mais à chaque sortie majeure, ne serait’il pas possible de rendre au moins "un" plugins-dist optionnel ?

  Pour le moment, en spip 3.3 [24240], il y a comme plugins-dist https://zone.spip.net/trac/spip-zone/browser/spip-zone/_core_/plugins
  Mais tous ne sont pas obligatoirement installer avec la dist (grenier, ?)
  Faudrait rayer les plugs qui sont en options

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