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• FFMPEG segment live video for DASH

  23 décembre 2014, par static

  I’m trying to stream live capture of desktop to my own server, which shall create an MPD with segment template for use with dash.js player.
  Using the following command i managed to get it working
  

  ffmpeg -rtbufsize 6M -f x11grab -s 1366x768 -r 10 -i :0.0 -flags +global_header \
  
  -vcodec libvpx -deadline realtime -profile:v 0 -keyint_min 1 -g 1 -cpu-used 0 \
  
  -vb 1200k -qmin 10 -qmax 42 -threads 4 -bufsize 6000k -slices 4 -map 0 -an \
  
  -f stream_segment -segment_time 2 -segment_format webm **/streams

  The output :

  Input #0, x11grab, from ':0.0': Duration: N/A, start: 1419329032.549498, bitrate: N/A
  
  Stream #0:0: Video: rawvideo (BGRA / 0x41524742), bgra, 1366x768, 10 fps, 10 tbr, 1000k tbn, 10 tbc
  
  [libvpx@ 0x23ccf60] v1.3.0 Output #0, stream_segment, ssegment, to /streams/d':
  
  Metadata:
  
  encoder : Lavf56.15.102
  
  Stream #0:0: Video: vp8 (libvpx), yuva420p, 1366x768, q=10-42, 1200 kb/s, 10 fps, 1k tbn, 10 tbc
  
  Metadata: encoder: Lavc56.13.100 libvpx
  
  Stream mapping: Stream #0:0 -> #0:0 (rawvideo (native) -> vp8 (libvpx))
  
  Press [q] to stop, [?] for help
  
  [swscaler @ 0x23ac0c0] Warning: data is not aligned! This can lead to a speedloss
  
  frame= 2839 fps= 10 q=0.0 Lsize=N/A time=00:04:43.90 bitrate=N/A
  
  video:135246kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

  If I increase the number of frames to produce better quality, the latency drastically increases and the stream is not in sync with the MPD. This is caused by the fact that keyframes are created at every frame -keyint_min 1 -g 1 because otherwise and error MEDIA_ERR_SRC_NOT_SUPPORTED is thrown by the player. This is probably because a keyframe must be found at the beginning of each segment.

  Could ffmpeg be used to generate keyframes as the first frame in each segment ? I try different values for -keyint_min x -g y, for example number of frames but with no result (probably because the number of frames stabilized after a couple a seconds, so the first 2-3 segments were produced with inconsistent number of frames, so all the keyframes were introduced in wrong positions in the segments).

• avformat/matroskadec : fix handling of recursive SeekHead elements

  6 décembre 2014, par wm4

  avformat/matroskadec : fix handling of recursive SeekHead elements
  When matroska_execute_seekhead() is called, it goes through the list of
  
  seekhead entries and attempts to read elements not read yet. When doing
  
  this, the parser can find further SeekHead elements, and will extend the
  
  matroska->seekhead list. This can lead to a (practically) infinite loop
  
  with certain broken files. (Maybe it can happen even with valid files.
  
  The demuxer doesn’t seem to check correctly whether an element has
  
  already been read.)
  Fix this by ignoring elements that were added to the seekhead field
  
  during executing seekhead entries.
  This does not fix the possible situation when multiple SeekHead elements
  
  after the file header (i.e. occur after the "before_pos" file position)
  
  point to the same elements. These elements will probably be parsed
  
  multiple times, likely leading to bugs.
  Fixes ticket #4162.
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavformat/matroskadec.c

• hdsenc : Clear the previous codec tag when setting up the chained muxer

  18 novembre 2014, par Martin Storsjö

  hdsenc : Clear the previous codec tag when setting up the chained muxer
  The chained flv muxer wants one set of tags - normally this set
  
  could be signaled via the AVOutputFormat codec_tag field (as
  
  smoothstreamingenc and dashenc do). hdsenc doesn’t signal it, since
  
  the FLV codec tag arrays aren’t exported from flvenc.c. This can
  
  lead to the caller keeping an original codec tag from the originating
  
  container here, which would then be a mismatch for the FLV muxer.
  
  Since we don’t really care about what codec tag the caller might
  
  have set, just clear it and let the lavf muxer layer set the right
  
  one for the chained FLV muxer later instead.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavformat/hdsenc.c