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Isn't video transcoding easily parallelizable? I mean just split the video into N equal parts (at keyframes) and divide the work.

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Not a video encoding expert, but for live streams you can't merge the output until you process all the N parts, so you introduce delays. And if any part of the input pipeline, like an overlay containing a logo or text, is generated dynamically i.e. not a static mp4, it basically counts as a live stream.

Yes, good point about live streams.

Why not cut the image in rectangles and process those simultaneously? Wouldn't that work for live streams? (There may be artefacts at the seams though?)

Yes, and we do, but that is not the slow part: https://en.wikipedia.org/wiki/Motion_compensation

And as for seams: https://en.wikipedia.org/wiki/Deblocking_filter

Thanks! Very informative! It's really a fascinating topic.

You are right, but first you ideally should perform scene change detection (to put keyframes at propper positions), and that alone takes quite some processing.

Exactly as some encoders (H264) have keyframes at intervals (e.g., every 30 frames) rather than where the action occurs.

As such, they are suboptimal by default if a lot of motion occurs.

> some encoders (H264)

What H.264 encoder are you using that does not have a scene change detection option?

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