IOS: Subscription update with replacing stream

[kirankumar-ravuri]

Added passing streamid to the sdk for updating subscription

[jianjunz]

Thanks for your contribution. But I'm not merging this PR at this time because this is a non-trivial feature enhancement. APIs need to be detailed designed. For example, server side allows to replace audio/video track only.

[JamesTerm]

@jianjunz I see this PR is delayed merging, and so I ask... what is a preferred way to discuss contributions (features) to determine beforehand if they are PR candidate vs. ones that are not... I will have some soon, but I wish to discuss them to see if they are PR candidates first... and for that matter which ones are candidates for 4.2 release. I only wish to do PR's if I know this is what we want for everyone.

[jianjunz]

Hi @JamesTerm, sorry for my late reply. IMHO, I'd prefer to open an issue before a large feature, so we can discuss its design and schedule, especially for those involves both client and server side changes. Perhaps we could create a new repository to track these feature requests. For some small changes, I think it's OK to just create a PR.
Other members may have their own opinions about the process for contributing a new feature.

[JamesTerm]

Thanks for reply I've created issue #141, as it is a large feature