New answers tagged file-formats
You can check that with MediaInfo. It will tell you exactly how much space each stream (in your case, the video and the audio stream) of a video takes up and give both the absolute and the relative (i.e. percentage) value! To get the average proportions of the audio stream, just check a few of your videos and calculate ...
There are variables you don't mention, but you can make a quick estimate based on the video bit rate and the audio bit rate. With (say) 4800Kb/s video and 48Kb/s audio, the audio represents 1% of the file.
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