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• avformat/hls : Fix regression with ranged media segments

  26 juillet 2016, par Anssi Hannula

  avformat/hls : Fix regression with ranged media segments
  Commit 81306fd4bdf ("hls : eliminate ffurl_* usage", merged in d0fc5de3a6)
  
  changed the hls demuxer to use AVIOContext instead of URLContext for its
  
  HTTP requests.
  HLS demuxer uses the "offset" option of the http demuxer, requesting
  
  the initial file offset for the I/O (http URLProtocol uses the "Range :"
  
  HTTP header to try to accommodate that).
  However, the code in libavformat/aviobuf.c seems to be doing its own
  
  accounting for the current file offset (AVIOContext.pos), with the
  
  assumption that the initial offset is always zero.
  HLS demuxer does an explicit seek after open_url to account for cases
  
  where the "offset" was not effective (due to the URL being a local file
  
  or the HTTP server not obeying it), which should be a no-op in case the
  
  file offset is already at that position.
  However, since aviobuf.c code thinks the starting offset is 0, this
  
  doesn’t work properly.
  This breaks retrieval of ranged media segments.
  To fix the regression, just drop the seek call from the HLS demuxer when
  
  the HTTP(S) protocol is used.
  

  • [DH] libavformat/hls.c

• lavu/timecode : clarify error msg for timecode_rate

  5 novembre 2017, par Gyan Doshi

  lavu/timecode : clarify error msg for timecode_rate
  The user-supplied value for timecode_rate in drawtext is rounded
  
  to nearest integer. So, a supplied value of 0.49 or lower is rounded to 0.
  
  This throws a misleading error message which says "Timecode frame rate must be
  
  specified". Changed message to account for values under one.
  Also noted supported framerates for drop TC.
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] doc/filters.texi
  • [DH] libavutil/timecode.c

• How Much H.264 In Each Encoder ?

  8 septembre 2010, par Multimedia Mike — General

  Thanks to my recent experiments with code coverage tools, I have a powerful new — admittedly somewhat specious — method of comparing programs. For example, I am certain that I have read on more than one occasion that Apple’s H.264 encoder sucks compared to x264 due, at least in part, to the Apple encoder’s alleged inability to exercise all of H.264′s features. I wonder how to test that claim ?

  Experiment
  Use code coverage tools to determine which H.264 encoder uses the most features.

  Assumptions

  • Movie trailers hosted by Apple will all be encoded with the same settings using Apple’s encoder.
  • Similarly, Yahoo’s movie trailers will be encoded with consistent settings using an unknown encoder.
  • Encoding a video using FFmpeg’s libx264-slow setting will necessarily throw a bunch of H.264′s features into the mix (I really don’t think this assumption holds much water, but I also don’t know what “standard” x264 settings are).

  Methodology

  • Grab a random Apple-hosted 1080p movie trailer and random Yahoo-hosted 1080p movie trailer from Dave’s Trailer Page.
  • Use libx264/FFmpeg with the ‘slow’ preset to encode Big Buck Bunny 1080p from raw PNG files.
  • Build FFmpeg with code coverage enabled.
  • Decode each file to raw YUV, ignore audio decoding, generate code coverage statistics using gcovr, reset stats after each run by deleting *.gcda files.

  Results

  • x264 1080p video : 9968 / 134203 lines
  • Apple 1080p trailer : 9968 / 134203 lines
  • Yahoo 1080p trailer : 9914 / 134203 lines

  I also ran this old x264-encoded file (ImperishableNightStage6Low.mp4) through the same test. It demonstrated the most code coverage with 10671 / 134203 lines.

  Conclusions
  Conclusions ? Ha ! Go ahead and jump all over this test. I’m already fairly confident that it’s impossible (or maybe just very difficult) to build a single H.264-encoded video that exercises every feature that FFmpeg’s decoder supports. For example, is it possible for a file to use both CABAC and CAVLC entropy methods ? If it’s possible, does any current encoder do that ?