Comment by CharlesW | Hacker News Reader

Comment by CharlesW | Hacker News Reader

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For anyone disappointed that Handbrake doesn't allow you to specify a final file size and automagically figure out the rest, calculating this is straightforward.

  average bitrate [kbps] = target size [kilobits] ÷ length [seconds]

Example: You have 2'48" file that you need to be 5GB or less.

  - 2'48" is 10,080s
  - 5GB = 40,000,000 kb
  - average bitrate = 40,000,000 kb ÷ 10,080s = 3,968 kbps
  - If audio is 256 kbps, average video bitrate should be 3,712 kbps or less

If anyone from the Handbrake team is reading, thank you for all of your work on Handbrake. <3

This calculation only works if you encode at constant bitrate.

I usually encode at constant quality. The output size heavily depends on the input video. So, I wrote a wrapper in python that parses the HandbrakeCLI output estimates the final size based on percent completed & the current output file size. Then I can stop early if I realize the file is gonna be huge / the output quality is so shitty that I have to bump the quality factor.

> This calculation only works if you encode at constant bitrate.

This will need to be your average bitrate over the entire file, but the bitrate doesn’t have to be constant. It can (and ideally should) vary widely between static scenes and action sequences, for example.

Average bitrate would only be possible with a 2pass encoding though, I believe.

Yes! Or if you’re a masochist, lots of trial or error.

Technically still a multipass encoding if you have to manually launch the encoder multiple times with different parameters.

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