What exactly does bitrate mean in an video/audio file?

audio video ffmpeg converter bitrate
Jobin Jose picture Jobin Jose · Sep 15, 2013 · Viewed 12.4k times · Source

I use ffmpeg to convert videos from one format to another. Is bitrate the only parameter which decides the output size of a video/audio file?

Answer

topo Reinstate Monica picture topo Reinstate Monica · Sep 15, 2013

Yes, bitrate is essentially what will control the file size (for a given playback duration). It is the number of bits used to represent each second of material.

However, there are some subtleties, e.g. :

  • a video file encoded at a certain video bitrate probably contains a separate audio stream, with a separately-specified bitrate
  • most file formats will contain some metadata that won't be counted towards the basic video stream bitrate
  • sometimes the algorithm will not actually aim to achieve the specified bitrate - for example, using the CRF factor. http://trac.ffmpeg.org/wiki/x264EncodingGuide explains how two-pass would be preferred if targeting a specific file size.

So you may want to do a little experimenting with a particular set of options for a particular file format.

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