Latency and bidirectionally predicted frames in VideoEncoder.

[riju]

VideoEncoder can increase coding efficiency by referencing future frames when coding a frame (eg. B-frames). However, this also increases latency since the future frames need to be decoded before the bidirectionally encoded frames. This is not desirable in all use cases such as video conferencing.

How about adding maxPredictionFrames -

dictionary VideoEncoderEncodeOptions {
  .. 
  unsigned long maxPredictionFrames;
};

which gives the maximum number of future frames to use for prediction. Setting maxPredictionFrames to 0 would disable B-frames altogether.

Related to #55 .

[kenchris]

Nit naming maxLong - I think it is unclear what long refers to, why not maxPredictionFrames

[chcunningham]

This naming has some overlap with #58, where the proposal is to have unsigned long max_prediction; as a restriction on GOP size. I feel like the name should mention "bi-directional" or "b" somewhere?

[chcunningham]

Triage note: marking 'extension' as this proposes to simply add a new member to the config dict.