Optimize bitstream buffer sizes with estimates

[YakoYakoYokuYoku]

I've noticed that OpenAPV uses bitstream buffers with a size of 128 mebibytes, which is not a quantity to ignore, while encoding to avoid potential issues of overflows. Ideally this number should be calculated according to average bitrate or a quantization parameter per what I understand instead of an arbitrary number. Meanwhile, decoding is a bit more flexible if packet sizes are known. An estimate can help when using a low or a high bitrate regardless.

[kpchoi]

Could you propose how to estimate the bistream buffer size properly?
We could discuss more in ths thread.
As you know, video codec has the variations of bitstream size according to each frame, and it is difficult to know even average bitrate if constant QP case.

[YakoYakoYokuYoku]

I'm skimming through the standard, albeit I have a few ideas in mind.

Could you propose how to estimate the bistream buffer size properly?

If APV does something like JPEG we could have an estimate in this fashion. If we have a quantization matrix then we could estimate a size reduction in proportion to what values are in it. If these are high then we can expect higher compression, otherwise, if they are low, that would be a lower amount of compression. Of course this is not fully foolproof as it could result in misses depending the data we are dealing with.

On the other hand, with bitrates, it's simply a calculation involving a ratio between them and frame rates. Really straightforward.

With both cases we also have to take side data into account.