Comment by dtf

Comment by dtf a day ago

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These release notes are very interesting! I spent a couple of weeks recently writing a ProRes decoder using WebGPU compute shaders, and it runs plenty fast enough (although I suspect Apple has some special hardware they make use of for their implementation). I can imagine this path also working well for the new Android APV codec, if it ever becomes popular.

The ProRes bitstream spec was given to SMPTE [1], but I never managed to find any information on ProRes RAW, so it's exciting to see software and compute implementations here. Has this been reverse-engineered by the FFMPEG wizards? At first glance of the code, it does look fairly similar to the regular ProRes.

[1] https://pub.smpte.org/doc/rdd36/20220909-pub/rdd36-2022.pdf

averne_ a day ago

Do you have a link for that? I'm the guy working on the Vulkan ProRes decoder mentionned as "in review" in this changelog, as part of a GSoC project.

I'm curious wrt how a WebGPU implementation would differ from Vulkan. Here's mine if you're interested: https://github.com/averne/FFmpeg/tree/vk-proresdec

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  • dtf a day ago

    I don't have a link to hand right now, but I'll try to put one up for you this weekend. I'm very interested in your implementation - thanks, will take a good look!

    Initially this was just a vehicle for me to get stuck in and learn some WebGPU, so no doubt I'm missing lots of opportunities for optimisation - but it's been fun as much as frustrating. I leaned heavily on the SMPTE specification document and the FFMPEG proresdec.c implementation to understand and debug.

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    • averne_ a day ago

      No problem, just be aware there's a bunch of optimizations I haven't had time to implement yet. In particular, I'd to remove the reset kernel, fuse the VLD/IDCT ones, and try different strategies and hw-dependent specializations for the IDCT routine (AAN algorithm, packed FP16, cooperative matrices).

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