Recherche avancée

Sur d’autres sites (8103)

• How to set time_base when muxing AVI with libavformat ?

  18 mai 2012, par Anastasia

  In my application I receive from a remote server synchronized video
  (mpeg4) and audio (mp3) and mux them to avi file. The video comes
  frame-by-frame, and the audio comes in small chunks, say 200-250 ms.
  Both video frames and audio chunks have timestamps in milliseconds.

  My question is how to set audio time_base and pts correctly ?
  For video I set time_base.num = framerate, time_base.den = 1 ; and
  calculate pts as follows :

    AVRational time_base_1kHz; 
  
    time_base_1kHz.num = 1; 
  
    time_base_1kHz.den = 1000; 
  
    packet.pts = av_rescale_q(timeStamp - baseTimeStamp_, time_base_1kHz, videoStream_->time_base); 

  where baseTimeStamp_ is the 1st timestamp of the stream.

  But if I try do similar calculation for audio, I don't get playable
  avi. If I always set to audio AV_NOPTS_VALUE, then avi has playable
  video, but no audio.

  So what are the correct values for audio time_base and pts's ?
  Do I set time_base and pts's for video correctly ?

• Why does FFMPEG adds up extra bit rate to video ? [migrated]

  5 juin 2012, par user735647

  I use FFMPEG (command line Input) to convert my videos to a specific output format. The problem I am facing is when I try to pass a constant bit rate(700 kbps) to FFMPEG, the result is an output video with a different bit rate(say 1000 kbps). This phenomenon occurs invariably for all videos.Why is this happening ? I need to maintain a constant bit rate. Can anyone help me out.

  My FFMPEG version is 0.5

  The command line parameter which I am passing to FFMPEG is,

  -i {inputfile}
  
  -b 700k -ab 64k
  
  -vcodec libx264
  
  -acodec libfaac -ac 2 -ar 44100
  
  -y -s 320x240 
  
  {outputfile}

  EDIT :

  I was able to force CBR with a fluctuation of 3% when I used the following parameters.

   ffmpeg -i myfile.avi
  
   -b 4000k -minrate 4000k 
  
   -maxrate 4000k -bufsize 1835k   out.m2v

  But when I used -maxrate and - minrate along with my parameter set I was not able to force CBR. My parameter set is as follows,

  -i {inputfile}
  
  -b 1200k -minrate 1200k 
  
   -maxrate 1200k -bufsize 1200k 
  
  -ab 64k -vcodec libx264
  
  -acodec libfaac -ac 2 -ar 44100
  
  -y -s 320x240 
  
  {outputfile}

  Why is this happening ?

• Make video out of pictures (no compression)

  17 avril 2014, par Hermilton

  I have 1000 png files as output from a simulation (total size of all png-files 44.2 MB), and I want to make a video where each frame is simply one png file.
  So it should be something like just concatenating the png files to one movie file.

  I already tried doing this with "ffmpeg"/"avconv" but I'm a novice in this programms, and my output videos turned out to be either way to large (700MB !) or just blurry compared to the pngs.