lossless x264 in 4:2:0?

[Thunderbolt8]

Is it possible to get lossless encoding with x264 in 4:2:0? Using MeGUI, when I set crf=0 then I automatically get a file in 4:4:4. With crf=1 it's still in 4:2:0.

[sneaker_ger]

Yes, it's possible. Probably that's already what's happening. The profile is called "High 4:4:4 Predictive" but it also supports 4:2:0. MediaInfo should show the distinction between the profile name and the actual subsampling.

[LoRd_MuldeR]

Lossless x264 uses/requires the "High 4:4:4 Predictive" (High 4:4:4) Profile. That's because the "Predictive Lossless Coding" feature, which x264 uses in lossless mode, is allowed in "High 4:4:4" Profile only:
https://de.wikipedia.org/wiki/H.264#Profile

That this profile also allows the "4:4:4" chroma format is a coincidence. It doesn't mean the that content necessarily needs to be in the "4:4:4" chroma format ;)

[Thunderbolt8]

well, for some reason my TV does not like the lossless files produced by x264. It plays stuff with CRF=1 fine despite e.g. the bitrate is also very high then. So I guess this cannot be the limitation. My TV also plays lossless x265 fine, apparently because it still is 4:2:0. but encoding x265 losslessly is too slow for me.

So there is a way to get x264 lossless mode to be in 4:2:0? If so, how?

[sneaker_ger]

Like we said: it already is. No special setting required. Did you look at MediaInfo like I said? If your TV does not support the lossless profile that's just the way it is. Can't be helped.

[LoRd_MuldeR]

Support for "Predictive Lossless Coding" (or "High 4:4:4 Predictive" profile in general) is pretty much non-existent in consumer-grade hardware decoders :scared:

You can not get "lossless" mode, as it has been implemented in x264, without "High 4:4:4 Predictive" profile. x264, in lossless mode, uses "Predictive Lossless Coding", which unavoidably bumps the profile requirement to "High 4:4:4 Predictive".

Even if x264 would falsely declare the "lossless" stream as some lower profile than "High 4:4:4 Predictive", the stream would still use "Predictive Lossless Coding" and thus it still would require a decoder capable of "Predictive Lossless Coding"...

(Also, while "crf=1" is not "true" lossless, in the mathematical sense, I very much doubt that you, or anybody, can actually see a difference between "crf=1" and "true" lossless)

[kabelbrand]

Your TV does support High profile but not High 4:4:4. Just stick to a visually lossless CRF 1 if you are aiming for device compatibility.

[benwaggoner]

Your TV does support High profile but not High 4:4:4. Just stick to a visually lossless CRF 1 if you are aiming for device compatibility.
Plus setting --vbv-bufsize and --vbv-maxrate to the appropriate max values for your Profile @ Level. CRF 1 can easily get too big for a compliant decoder to handle well.

HEVC does a lot better with the "nearly lossless" case as lossless coding units and transform skip are available in Main Profile. So you can get lossless frames or parts of a frame when RDO pays off ad VBV allows.