title: ffprobe shows bitrate of 0.0 or N/A for h264 stream
body: <p>I have a 11-minute .mkv file with a h264 video stream, taking up 184MB of space. I would like to reduce the size of this file. I figured I could just reduce the bit-rate. But ffprobe doesn't output any. In fact, it says the length of the file is calculated from the bitrate and thus could be inaccurate, but there's no bitrate either in the summary or in the [FORMAT] entry:</p>
  
  <pre><code>&gt; ffprobe -show_format file.mkv
  [matroska,webm @ 0x7f8e8084b200] Estimating duration from bitrate, this may be inaccurate
  Input #0, matroska,webm, from 'file.mkv':
    Duration: 00:11:11.59, start: 0.000000, bitrate: N/A
      Stream #0.0: Video: h264 (High), yuv420p, 1280x720 [PAR 1:1 DAR 16:9], 29.97 fps, 29.97 tbr, 1k tbn, 59.94 tbc (default)
      Stream #0.1: Audio: aac, 48000 Hz, 5.1, s16 (default)
  [FORMAT]
  ...
  bit_rate=0.000000 
  [/FORMAT]
  </code></pre>
  
  <p>Thank you.</p>
  
  <p>EDIT: My understanding is that H.264 is a protocol. As such, I cannot tell, based on the ffprobe documentation, what implementation the h264 codec uses. If anyone knows that, I'd be grateful.</p>