Update codec builder to support rate limiting while running about mediadevices

[lherman-cs]

@at-wat what do you think about the interface?

[at-wat]

I think updating BaseParams.KeyFrameInterval is less meaningful on WebRTC (and also pure RTP) in which RTCP PictureLossIndication packet triggers a key frame.
I'm not very sure it's better to update whole BaseParams.

[lherman-cs]

From my understanding, setting BaseParams.KeyFrameInterval to 0 means the same thing with force keyframe. Did I misunderstand this?

[at-wat]

I think BaseParams.KeyFrameInterval=0 means that all frames are key frame.
PictureLossIndication makes next single frame into key frame.

[lherman-cs]

Ah, that makes total sense. I guess nvm then, I think we can use what you've suggested already,

package codec

import "io"

type ReadCloser interface {
	io.ReadCloser
	SetBitRate(int) error
	ForceKeyFrame() error
}

What do you think about the naming? I changed it from StreamReader to ReadCloser because I think it's more common and it's clear that's different from io.ReadCloser, because it'll be called with the namespace codec.ReadCloser. This pattern also exists in the standard library, there are image.Image and draw.Image. The main difference is that draw.Image has an extra method that allows setting a single pixel to a color.

[at-wat]

codec.ReadCloser sounds good to me!

[at-wat]

related: https://github.com/pion/webrtc/wiki/MediaAPI#rtpsender-will-have-callbacks-for-rtcp-feedback-results

[EmrysMyrddin]

Is this still in progress ?

I came across this issue will trying to understand how PLI packets are handled in pion's webrtc. From what I understand of the code, receiving a PLI should trigger a new key frame, but this is not implemented for now right ?

Related to this, I have made a PR to implement key frame request for VPX: #334

[EmrysMyrddin]

This is stale and no longer applicable since #338 has been merged.