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• Transcoding fMP4 to HLS while writing on iOS using FFmpeg

  29 avril 2017, par bclymer

  TL ;DR

  I want to convert fMP4 fragments to TS segments (for HLS) as the fragments are being written using FFmpeg on an iOS device.

  Why ?

  I’m trying to achieve live uploading on iOS while maintaining a seamless, HD copy locally.

  What I’ve tried

  1. Rolling AVAssetWriters where each writes for 8 seconds, then concating the MP4s together via FFmpeg.

     What went wrong - There are blips in the audio and video at times. I’ve identified 3 reasons for this.

     1) Priming frames for audio written by the AAC encoder creating gaps.

     2) Since video frames are 33.33ms long, and audio frames 0.022ms long, it’s possible for them to not line up at the end of a file.

     3) The lack of frame accurate encoding present on Mac OS, but not available for iOS Details Here

  2. FFmpeg muxing a large video only MP4 file with raw audio into TS segments. The work was based off the Kickflip SDK

     What Went Wrong - Every once in a while an audio only file would get uploaded, with no video whatsoever. Never able to reproduce it in-house, but it was pretty upsetting to our users when they didn’t record what they thought they did. There were also issues with accurate seeking on the final segments, almost like the TS segments were incorrectly time stamped.

  What I’m thinking now

  Apple was pushing fMP4 at WWDC this year (2016) and I hadn’t looked into it much at all before that. Since an fMP4 file can be read, and played while it’s being written, I thought that it would be possible for FFmpeg to transcode the file as it’s being written as well, as long as we hold off sending the bytes to FFmpeg until each fragment within the file is finished.

  However, I’m not familiar enough with the FFmpeg C API, I only used it briefly within attempt #2.

  What I need from you

  1. Is this a feasible solution ? Is anybody familiar enough with fMP4 to know if I can actually accomplish this ?
  2. How will I know that AVFoundation has finished writing a fragment within the file so that I can pipe it into FFmpeg ?
  3. How can I take data from a file on disk, chunk at a time, pass it into FFmpeg and have it spit out TS segments ?

• Transcoding fMP4 to HLS while writing on iOS using FFmpeg

  12 juillet 2017, par bclymer

  TL ;DR

  I want to convert fMP4 fragments to TS segments (for HLS) as the fragments are being written using FFmpeg on an iOS device.

  Why ?

  I’m trying to achieve live uploading on iOS while maintaining a seamless, HD copy locally.

  What I’ve tried

  1. Rolling AVAssetWriters where each writes for 8 seconds, then concatenating the MP4s together via FFmpeg.

     What went wrong - There are blips in the audio and video at times. I’ve identified 3 reasons for this.

     1) Priming frames for audio written by the AAC encoder creating gaps.

     2) Since video frames are 33.33ms long, and audio frames 0.022ms long, it’s possible for them to not line up at the end of a file.

     3) The lack of frame accurate encoding present on Mac OS, but not available for iOS Details Here

  2. FFmpeg muxing a large video only MP4 file with raw audio into TS segments. The work was based on the Kickflip SDK

     What Went Wrong - Every once in a while an audio only file would get uploaded, with no video whatsoever. Never able to reproduce it in-house, but it was pretty upsetting to our users when they didn’t record what they thought they did. There were also issues with accurate seeking on the final segments, almost like the TS segments were incorrectly time stamped.

  What I’m thinking now

  Apple was pushing fMP4 at WWDC this year (2016) and I hadn’t looked into it much at all before that. Since an fMP4 file can be read, and played while it’s being written, I thought that it would be possible for FFmpeg to transcode the file as it’s being written as well, as long as we hold off sending the bytes to FFmpeg until each fragment within the file is finished.

  However, I’m not familiar enough with the FFmpeg C API, I only used it briefly within attempt #2.

  What I need from you

  1. Is this a feasible solution ? Is anybody familiar enough with fMP4 to know if I can actually accomplish this ?
  2. How will I know that AVFoundation has finished writing a fragment within the file so that I can pipe it into FFmpeg ?
  3. How can I take data from a file on disk, chunk at a time, pass it into FFmpeg and have it spit out TS segments ?

• FFmpeg Has A Native VP8 Decoder

  24 juin 2010, par Multimedia Mike — VP8

  Thanks to David Conrad and Ronald Bultje who committed their native VP8 video decoder to the FFmpeg codebase yesterday. At this point, it can decode 14/17 of the VP8 test vectors that Google released during the initial open sourcing event. Work is ongoing on those 3 non-passing samples (missing bilinear filter). Meanwhile, FFmpeg’s optimization-obsessive personalities are hard at work optimizing the native decoder. The current decoder is already profiled to be faster than Google/On2’s official libvpx.

  Testing
  So it falls to FATE to test this on the ridiculous diversity of platforms that FFmpeg supports. I staged individual test specs for each of the 17 test vectors : vp8-test-vector-001 ... vp8-test-vector-017. After the samples have propagated through to the various FATE installations, I’ll activate the 14 test specs that are currently passing.

  Initial Testing Methodology
  Inspired by Ronald Bultje’s idea, I built the latest FFmpeg-SVN with libvpx enabled. Then I selected between the reference and native decoders as such :

  $ for i in 001 002 003 004 005 006 007 008 009 \
   010 011 012 013 014 015 016 017
  do
    echo vp80-00-comprehensive-$i.ivf
    ffmpeg -vcodec libvpx -i \
      /path/to/vp8-test-vectors-r1/vp80-00-comprehensive-$i.ivf \
      -f framemd5 - 2> /dev/null
  done > refs.txt
  $ for i in 001 002 003 004 005 006 007 008 009 \
  
   010 011 012 013 014 015 016 017
  
  do
  
    echo vp80-00-comprehensive-$i.ivf
  
    ffmpeg -vcodec vp8 -i \
  
      /path/to/vp8-test-vectors-r1/vp80-00-comprehensive-$i.ivf \
  
      -f framemd5 - 2> /dev/null
  
  done > native.txt
  $ diff -u refs.txt native.txt
  

  That reveals precisely which files differ.