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The thing is that 4:2:0 chroma is the default in most codecs because the main profiles only support that. You couldn't stream full chroma video on twitch even

The thing is that 4:2:0 chroma is the default in most codecs because the main profiles only support that. You couldn't stream full chroma video on twitch even if you wanted to. And subsampled chroma looks terrible on colored text, edges between flat colored areas and similar things.[0] So 4:4:4 is a must, only once you have that you can think about adaptive quantization for chroma. [0] https://upload.wikimedia.org/wikipedia/commons/1/1c/420-progressive-still.png https://upload.wikimedia.org/wikipedia/commons/1/1c/420-prog...

vardump 9y ago
I agree with that, but 4:4:4 also means there's twice as much data. I think you should be able to get away with using chroma subsampling for moving portions while allocating bits in data stream for stationary areas, without subsampling (by using some heuristics, perhaps.) Chroma from luma techniques might be interesting in this context. https://people.xiph.org/~xiphmont/demo/daala/demo4.shtml https://people.xiph.org/~xiphmont/demo/daala/demo4.shtml
- clouddrover 9y ago
  Chroma from luma happens to work particularly well for video game content. It's one of the reasons Twitch is interested in using AV1 as soon as possible. Here's a talk by Thomas Daede where he discusses chroma from luma: https://www.youtube.com/watch?v=yKEDf5-2sT4 https://www.youtube.com/watch?v=yKEDf5-2sT4 Slides: https://people.xiph.org/~tdaede/demuxed_av1_2017.pdf https://people.xiph.org/~tdaede/demuxed_av1_2017.pdf Twitch is also interested in AV1 for its s-frames feature which allows for better compression in low latency live streaming: https://www.youtube.com/watch?v=o5sJX6VA34o https://www.youtube.com/watch?v=o5sJX6VA34o https://www.youtube.com/watch?v=AeSNW2T7QwE https://www.youtube.com/watch?v=AeSNW2T7QwE
- brigade 9y ago
  4:4:4 doesn’t mean twice the compressed bitrate, however. First, chroma residual already takes a minority of bits - luma residual and prediction info take way more bits and those are unchanged going to 4:4:4. Second, quantizing chroma more so there’s the same number of chroma bits as there would have been in 4:4:4 is approximately equivalent as subsampling chroma in the first place (okay, its actually slightly worse, so yeah you need maybe 1% greater bitrate to match quality with 4:2:0 with modern codecs on sequences for which 4:2:0 subsampling is transparent.)

vardump 9y ago

I agree with that, but 4:4:4 also means there's twice as much data. I think you should be able to get away with using chroma subsampling for moving portions while allocating bits in data stream for stationary areas, without subsampling (by using some heuristics, perhaps.) Chroma from luma techniques might be interesting in this context. https://people.xiph.org/~xiphmont/demo/daala/demo4.shtml https://people.xiph.org/~xiphmont/demo/daala/demo4.shtml

clouddrover 9y ago
Chroma from luma happens to work particularly well for video game content. It's one of the reasons Twitch is interested in using AV1 as soon as possible. Here's a talk by Thomas Daede where he discusses chroma from luma: https://www.youtube.com/watch?v=yKEDf5-2sT4 https://www.youtube.com/watch?v=yKEDf5-2sT4 Slides: https://people.xiph.org/~tdaede/demuxed_av1_2017.pdf https://people.xiph.org/~tdaede/demuxed_av1_2017.pdf Twitch is also interested in AV1 for its s-frames feature which allows for better compression in low latency live streaming: https://www.youtube.com/watch?v=o5sJX6VA34o https://www.youtube.com/watch?v=o5sJX6VA34o https://www.youtube.com/watch?v=AeSNW2T7QwE https://www.youtube.com/watch?v=AeSNW2T7QwE
brigade 9y ago
4:4:4 doesn’t mean twice the compressed bitrate, however. First, chroma residual already takes a minority of bits - luma residual and prediction info take way more bits and those are unchanged going to 4:4:4. Second, quantizing chroma more so there’s the same number of chroma bits as there would have been in 4:4:4 is approximately equivalent as subsampling chroma in the first place (okay, its actually slightly worse, so yeah you need maybe 1% greater bitrate to match quality with 4:2:0 with modern codecs on sequences for which 4:2:0 subsampling is transparent.)