8 ms·

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 enou

by dtf 1y ago

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

averne_ 1y 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 https://github.com/averne/FFmpeg/tree/vk-proresdec
- dtf 1y 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.
  - averne_ 1y 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).
emersion 1y ago
Pretty much reverse engineered: https://mk.pars.ee/notes/a9ihgynpvdo6003w https://mk.pars.ee/notes/a9ihgynpvdo6003w

by dtf 1y ago

averne_ 1y 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 https://github.com/averne/FFmpeg/tree/vk-proresdec

dtf 1y 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.
- averne_ 1y 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).

emersion 1y ago

Pretty much reverse engineered: https://mk.pars.ee/notes/a9ihgynpvdo6003w https://mk.pars.ee/notes/a9ihgynpvdo6003w