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• what is the name of the video codec that could dynamic adjust resolution and FPS

  29 novembre 2015, par user454083

  I remember that there is video codec could dynamic adjust frame rate and resolution.
  For example, sender side, always send a base profile with QQVGA with 15 FPS, and receiver side always could at least decode QQVGA with 15 FPS. As long as there is more capacity in the bandwidth or CPU process time, sender side could add more details on the pixel of each frame. For example, add more details in the QQVGA, then new frame can be decoded as QVGA or VGA. And insert frames between frames in base profile. The 15 FPS can be 30 FPS etc..
  I wonder what is the name of this codec. If I remember it correctly, YouTube uses this codec and Google holds the patent of this video codec.

  If someone could remind me what is the name of this codec and more details of this codec. thanks

• How to decrease latency of images based live streaming ?

  18 octobre 2020, par Xiaofeng

  I need to encode and stream live images, but there is always about a 3s latency, how to decrease it ?

  


  The live stream is generated by the following command

  


  ffmpeg -analyzeduration 0 -probesize 32 -i h264_rtsp_url \
       -vf fps=1 -fflags nobuffer -fflags flush_packets -f mjpeg - \
    | ffmpeg -r 1 -f image2pipe -analyzeduration 0 -probesize 32 -i - \
             -c:v libx264 -pix_fmt yuv420p -tune zerolatency \
             -force_key_frames "expr:gte(t,n_forced*1)" \
             -flags low_delay -fflags nobuffer -fflags flush_packets \
             -profile:v main -preset medium -r 15 \
             -f rtp_mpegts rtp://127.0.0.1:4001


  


  Changing preset from medium to ultrafast does not affect the result, still 3s latency.

  


  And I am using mpv to play the streams,
The stream encoded by images :

  


  mpv --profile='low-latency' \
    --untimed --no-cache --no-demuxer-thread --vd-lavc-threads=1 \
    rtp://127.0.0.1:4001


  


  The origin stream :

  


  mpv --profile='low-latency' \
    --untimed --no-cache --no-demuxer-thread --vd-lavc-threads=1 \
    h264_rtsp_url


  


  [1] https://trac.ffmpeg.org/wiki/StreamingGuide

  


• avcodec/vc1dec : Re-order init to avoid initting hwaccel too early

  8 août 2015, par Philip Langdale

  avcodec/vc1dec : Re-order init to avoid initting hwaccel too early
  At least for vdpau, the hwaccel init code tries to check the video
  
  profile and ensure that there is a matching vdpau profile available.
  If it can’t find a match, it will fail to initialise.
  In the case of wmv3/vc1, I observed initialisation to fail all the
  
  time. It turns out that this is due to the hwaccel being initialised
  
  very early in the codec init, before the profile has been extracted
  
  and set.
  Conceptually, it’s a simple fix to reorder the init code, but it gets
  
  messy really fast because ff_get_format(), which is what implicitly
  
  trigger hwaccel init, is called multiple times through various shared
  
  init calls from h263, etc. It’s incredibly hard to prove to my own
  
  satisfaction that it’s safe to move the vc1 specific init code
  
  ahead of this generic code, but all the vc1 fate tests pass, and I’ve
  
  visually inspected a couple of samples and things seem correct.
  Signed-off-by : Philip Langdale <philipl@overt.org>
  

  • [DH] libavcodec/vc1dec.c