Provide Surface API for reading back the configured encoding bitrate(s)

[yellowdoge]

Section MediaRecorder Properties says:

[TO DO: Provide API surface to set and read these. When that is done, this section will be removed.]

this is the issue for that TODO, for the bitrate options concretely.

(It's basically a follow up of @mreavy "improve bitrate control in MediaRecorder" #20 - discussed with @tdaede).

[mreavy]

That looks good, except that the three bitrate properties should all use the same or similar language to say that the target bitrate isn't guaranteed. I'll close #20

[yellowdoge]

@mreavy, re. your comment, from https://rawgit.com/w3c/mediacapture-record/master/MediaRecorder.html#dictionary-mediarecorderoptions-members,

• audioBitsPerSecond: This is a hint for the encoder and the value might only be achieved over a long time.
• videoBitsPerSecond : This is a hint for the encoder and the value might be surpassed or not achieved.
• bitsPerSecond: This parameter is a hint for the encoder(s) and the total value might be surpassed or not achieved at all.

[mreavy]

@miguelao :I'm sorry, I don't see a question here - those are the descriptions that need to be synchronized, yes.

[yellowdoge]

Oh I see, you meant that the three should say a similar thing, gotcha.

[yellowdoge]

Closed as per #47