Re: [mediacapture-record] Allow updating audioBitsPerSecond and videoBitsPerSecond as done for mimeType (#205)

> > In a case of sync vs async w3c seems to prefer sync if at all feasible. I am not sure I see how deciding a default bitrate is an async getter attached to an OS resource. Are there hardware encoders one may not configure the bitrate of?
> 
> The fact that RTCRtpSender.getCapabilities is providing a synchronous API is an identified issue, see [w3c/webrtc-extensions#49](https://github.com/w3c/webrtc-extensions/issues/49)
> 
> If it is difficult to know which encoder (or which profiles) are supported, it is not easy to select a good default bit rate.
> Also, for video, the frame size might have a potential impact on a good default bit rate.

For some definition of "good", sure. I do believe a decent default bit rate could be found either way.
The same problem exists for a video track which is initially low resolution and later sees an increased resolution of several magnitudes, since there is no API to change the bitrate on the fly.

> In the case of passthrough codecs, it seems that we would like the bit rate to be set to 0 (?).

The bitrate attributes are not really covered well in the spec for passthrough, but the spec does mention that the UA will have to be prepared to fall back to re-encoding, should the source used for passthrough change codec on the fly. After it falls back, and the bitrate attributes were 0 because of passthrough, what are the bitrate attributes supposed to be now? Perhaps it's better to say that with passthrough the bitrate attributes will be ignored. Or that if the configured bitrate is lower than the bitrate of the passthrough source, the UA may re-encode anyway, to match.

> Are we sure though that we can know synchronously that passthrough codecs will be supported for all remote tracks?

Why do we need to know that?

-- 
GitHub Notification of comment by Pehrsons
Please view or discuss this issue at https://github.com/w3c/mediacapture-record/issues/205#issuecomment-712396900 using your GitHub account


-- 
Sent via github-notify-ml as configured in https://github.com/w3c/github-notify-ml-config

Received on Monday, 19 October 2020 19:36:39 UTC