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• Is it possible to undo temporal compression by reconstructing I-frames from B or P frames ?

  8 avril 2021, par connor449

  Is it possible to convert P or B frames back into I-frames ?

  


  This post suggest its possible via transcoding, but I do not understand the solution at all.

  


  Create I Frame out of P and B frames

  


  I am trying to take a video with I/P/B frames and reconstruct it to a I/I/I, like a MotionJPEG video.

  


• ffmpeg compression takes a long time

  31 mars 2021, par yesterday

  I'm using the following ffmpeg command in a react-native project to convert and compress a mov-file to a mp4-file. The command works, but it takes +1m30sec to convert a clip of only 10 seconds. Before I did a simple copy (because afaik mov and mp4 have the same codecs), and this copy was pretty fast (almost instantaneous for a 10sec clip).

  


  My command :

  


  ffmpeg -i input.mov -vcodec h264 -acodec mp3 -preset ultrafast output.mp4


  


  My previous command :

  


  ffmpeg -i input.mov -c copy -preset ultrafast output.mp4


  


  The preset ultrafast seems not to work with the first command.

  


• adaptive compression with ffmpeg

  3 février 2016, par paunescuionica

  I’m currently developing an application which will enable visualizing images from different sources (mostly IP cameras) in browser (in a HTML5 video element). The UI will allow for matrix view so, normally 16 or more cameras will be displayed at the same time.
  From cameras I get MJPEG streams or JPEG images (which I "convert" to MJPEG streams). So, for a camera, I have an MJPEG stream which I set as input for ffmpeg. I instruct ffmpeg to convert this to MP4 & H.264, and expose the output as a tcp stream, like this :

  ffmpeg -f mjpeg -i "http://localhost/video.mjpg" -f mp4 -vcodec libx264 "tcp ://127.0.0.1:5001 ?listen"

  This works just fine on localhost, I get the stream displayed in the web page, at best quality.

  But this has to work in various network conditions. I played a bit with chrome throttling settings, and noticed that if the network speed is just a bit below the required speed (given by the current compression settings I use in ffmpeg), the things start to go wrong : from stream start being delayed (so, no longer a live stream), up to complete freeze of ’live’ image in browser.

  What I need is an "adaptive" way to do the compression, in relation with current network speed.

  My questions are :

  • is ffmpeg able to handle this, to adapt to network conditions - automatically reduce compression quality when speed is low ; so the image in browser will be lower quality, but live (which is most important in my case)

  • if not, is there a way to workaround this ?

  • is there a way to detect the network bottleneck ? (and then restart ffmpeg with lower compression parameters ; this is not a dynamic adaptive streaming, but better than nothing)

  Thank you in advance !