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• Accurately calculate concatenated audio file size without actually concatenating for rss enclosure length

  19 décembre 2024, par askrill

  A little background. Im working on implementing DAI into a podcast hosting and the solution I’m working with is splitting the audio file for mid role ads and then just concatenating the files with the ad in middle. All files will be the same encoding, bitrate… what I need to figure out is what to put as the length of the encloser in the rss feed. In addition if the ad is gonna change per request then there’s no way to keep that encloser length accurate unless all the ads are the same size.

  


• avformat/matroskadec : Accept more unknown-length elements

  17 mai 2019, par Andreas Rheinhardt

  avformat/matroskadec : Accept more unknown-length elements
  The current Matroska specifications mandate that only two elements may
  
  use an unknown-length length : Segments and clusters. But this was not
  
  always so : For the greater part of Matroska's existence, all master
  
  elements were allowed to make use of the unknown-length feature.
  And there were muxers creating such files : For several years
  
  libavformat's Matroska muxer used unknown-length for all master
  
  elements when the output wasn't seekable. This only stopped in March
  
  2010 with 2529bb30. And even afterwards it was possible (albeit
  
  unlikely) for libavformat to create unknown-length master elements
  
  that are in violation of today's specifications, namely if the master
  
  element was so big that the seek backwards to update the size could
  
  no longer be performed inside the AVIOContext's write buffer. This
  
  has only been fixed in October 2016 (with the patches that introduced
  
  support for writing CRC-32 elements).
  Libavformat's Matroska demuxer meanwhile has never really supported
  
  unknown-length elements besides segments and clusters. Support for the
  
  latter was hardcoded. This commit changes this : Now all master elements
  
  for which a syntax to parse them is available are supported. This
  
  includes the files produced by old versions of libavformat's muxer.
  More precisely, master elements that have unknown length and are about
  
  to be parsed (not skipped) are supported ; only a warning is emitted for
  
  them. For normal files, this means that level 1 elements after the
  
  clusters that are encountered after the clusters have been parsed (i.e.
  
  not because they are referenced by the seekhead at the beginning of the
  
  file) are still unsupported (they would be skipped at this point if
  
  their length were known).
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskadec.c

• ffmpeg : setting framerate changes also length

  21 février 2020, par planetmaker

  I’m creating videos from images sequences and I’d like to set the desired framerate of the resulting video file by the -r FPS flag with commands like

  ffmpeg -i %05d.bmp -r 30 -c:v h264 -vframes 780 -qscale:v 0 output.mp4

  However it seems that it does make a difference whether I set -r 30 or -r 60 in as much that the video ends earlier (thus less than specified 780 input images are used) the higher I set the framerate.

  The folder contains thousands of sequential images which follow the specified scheme %05d.bmp and I only need the first fixed-length part of this sequence - but at a higher frame rate than the default rate of 30fps.

  What part do I miss when trying to use the frame rate ? How do I set the FPS to a higher value but retaining the input length ?