Quote:
Originally Posted by benwaggoner
No suggestion of what happens if higher or lower values are used.
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It means more frames in memory, so especially at higher resolution (1080p/4k) and/or high bitdepth (10bit/HDR), this can significantly affect memory usage. You'll have to do your own measurements on how much exactly, but frames-in-memory (along with their associated metadata) tend to be one of the biggest memory consumers in encoders, so you want to keep this low if you can.
However, on the flip-side, this is used for adaptive/predictive encoding decision making, i.e. better quality and/or better quality/speed ratio (see "tpl" in various parts of the codebase, which means "temporal"). At minimum, this should be a few frames larger than the max. alt-ref frame group size (32? I think), but larger will be better (with diminishing returns). For real-time/low-latency coding, you can set this to 1, but it means no out-of-order frame coding.