title: avcodec/avformat Number of Frames in File
body: <p>I need to know how to find the total number of frames in a video file using avcodec/avformat.</p>
  
  <p>I have a project that I'm picking up from someone else who was using the ffmpeg libraries to decode video streams. I need to retrofit some functionality to seek around frame by frame, and so my first task is to simply figure out the total number of frames in the file. AVStream.nb_frames seems to be a reasonable place to look, but this is always 0 with all of the video files I've tried.  Is deducing the total number of frames from AVFormatContex.duration the best way to go?</p>