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• avformat/matroskaenc : Simplify writing Cues

  30 décembre 2019, par Andreas Rheinhardt

  avformat/matroskaenc : Simplify writing Cues
  When the Matroska muxer writes the Cues (the index), it groups index
  
  entries with the same timestamp into the same CuePoint to save space.
  
  But given Matroska's variable-length length fields, it either needs
  
  to have an upper bound of the final size of the CuePoint before writing it
  
  or the CuePoint has to be assembled in a different buffer, so that after
  
  having assembled the CuePoint (when the real size is known), the CuePoint's
  
  header can be written and its data copied after it.
  The first of these approaches is the currently used one. This entails
  
  finding out the number of entries in a CuePoint before starting the
  
  CuePoint and therefore means that the list is read at least twice.
  
  Furthermore, a worst-case upper-bound for the length of a single entry
  
  was used, so that sometimes bytes are wasted on length fields.
  This commit switches to the second approach. This is no longer more
  
  expensive than the current approach if one only resets the dynamic
  
  buffer used to write the CuePoint's content instead of opening a new
  
  buffer for every CuePoint : Writing the trailer of a file with 540.000
  
  CuePoints improved actually from 219054414 decicycles to 2164379394
  
  decicycles (based upon 50 iterations).
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• libva-dev not available for 32 bit ? "ERROR : vaapi not found"

  7 août 2013, par user2593271
  • I'm trying to configure ffmpeg library for ubuntu for 32 bit.
  • Earlier it wasn't compiling for both 32 and 64 bit.
  • It was throwing this error "ERROR : vaapi not found".
  • Then I installed libav-dev and it configures for 64 bit.
  • Can't find 32 bit lib for libva-dev. Anybody knows how to approach ?

• ffplay startup time proportional to specified framerate

  17 décembre 2019, par bremen_matt

  I am playing a video over http using ffplay. The call I am using looks like this :

  ffplay -framerate 30 -fflags nobuffer -flags low_delay -autoexit -i http://localhost:8880

  The video is an H.264 encoding where (my understanding is a bit unclear here) it is something like a "raw" H.264 stream without timestamps.

  My primary concern is to get video displayed with low latency. In that regard, the video is fine.

  The issue is with the framerate and with the startup time.

  The video source is emitting frames as soon as they are processed, so the frame rate is not constant. However, my experience is that as long as you specify a framerate larger than the max achievable frame rate of the source, then the viewer still looks fine. On the flipside, if the video source starts emitting frames at 60 fps, but I specify a framerate of 30, then the delay just sort of builds up in ffplay to the point where after 10 seconds, the video is 20 seconds behind. So the first question would be whether there is a way to get ffplay to use a variable framerate. The behavior I am looking for is "display a frame as soon as it is received over http".

  In light of the aforementioned issue, the approach I have been taking is to simply specify a high framerate, which seems to work. However, there is an issue with this approach in the form of startup time. When I set the framerate to 10, the ffplay window starts in approx 3 seconds, but then quickly starts accruing a lag (so I can’t do this). When I set the framerate to 100, the ffplay window takes 30 seconds (literally 30 seconds) to start, but then will not have any lag.

  I have seen that ffmpeg has a vsync option that on the surface seems like it would allow you to set a variable framerate. However, ffplay doesn’t seem to recognize this. I would also be willing to pipe the output of ffmpeg to a different window (I am running Ubuntu 18.04) if that is what must be done, but I would prefer not to have to recompile ffplay.