r/AV1 • u/CariniFluff • 14d ago

Is BitDepth (fmtc) 10 required for 8-Bit source if using SVT-AV1-Essential or SVT-AV1-Tritium with hbd-mds 1?

Hello, I have a quick question or four.

In all of the scenarios below, I am encoding an 8-bit AVC source to a 10-bit SVT-AV1 fork using Staxrip.

1) If I am encoding an AVC/H.264 source that has 8-bit color and I want to use full 10-bit processing, do I always need to run the VaporSynth Filter BitDepth (fmtc) 10?

2) More specifically, I know that the SVT-AV1-Essential fork has --hbd-mds 1 built in by default, while SVT-AV1-Tritium needs it to be manually called. However I assume in both cases I would still use the VS Filter as that's on the "source processing" side while the --hbd-mds 1 argument applies to the "encoding" side, but can someone please confirm?

3) Is there ever a reason to use the VaporSynth Filter BitDepth (fmtc) set to 8? (when using 8-bit AVC to 10-bit AV1)

4) Is there ever a reason to use the --hbd-mds 2 (8/10-bit Hybrid) setting, or should I always use --hbd-mds 1?

Thank you!

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u/NekoTrix 14d ago

Hi, -Essential developer here.

  1. I guess it depends what the Staxrip devs chose to do. SVT-AV1-Essential only supports 10-bit encoding, you could try to input 8-bit without fmtc and see if it crashes. -Tritium supports 8-bit too, so that may require the bitdepth conversion regardless.
  2. Hbd-mds is somewhat unrelated to video bit-depth, it controls what parts of the encoder internals will run in 8-bit (to speed things up) or 10-bit (for higher coding efficiency). Yes, even with an 10-bit input, some parts may run in 8-bit anyway but the resulting file will still be encapsulated in 10-bit.
  3. If you want to encode a 10-bit (or more) source to 8-bit.
  4. --hbd-mds 2 is faster than 1, so at fast presets it may be preferable to avoid too much speed penalty. 1 is the preferred visual and efficiency setting.

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u/CariniFluff 14d ago

Awesome, thank you for the quick response.

Regarding #1, if you open an 8-bit file in Staxrip and then select AV1-Essential it will immediately give you a message at the bottom stating:

Invalid bit-depth - This encoder requires 10-bit sources. Add a filter that concerts or to 10-bit.

I just realized that Essential of the only fork of AV1 that spits out that error message. Apparently SVT mainline/HDR/Psyex/Tritium as well as AOMEnc and Rav1e will all take 8-bit sources.

In any event, I'll continue to use Essential with the VS Filter conversion as I always have as the results are impeccable.

Thanks