ISDK-2863, ISDK-2355, ISDK-2903: Update ReplayKitExample for 3.4.0, improve video quality

[ceaglest]

This PR makes several changes to improve the quality of ReplayKit content.

• VP8 screencast is now the default for iPhones in an extension. H.264 is more efficient but does not provide great quality in screencast mode. In video mode downscaling can often occur with detailed iOS UI
• Reduced memory usage in an extension
  • Input makes a downscaled copy of frames
  • Return RPIOSurface to Apple as soon as possible after downscaling it
  • Disabled insights when VP8 is being used (~512 KB)
  • Disable frame retransmissions when screencast is used (~4 MB on iPad)
  • Audio publication is optional (~512 KB)
• ISDK-2355: Added CoreImagePixelBufferInput to solve image tearing / vsync problems
  • CVPixelBufferPool used to ensure 1 frame in-flight to the encoder at a time
  • Adjusted scaling to find an acceptable balance for text readability
  • CIContext reads the IOSurface in a synchronized manner, it appears to be a private API
  • Not enabled for iPad / extension use case due to extra memory required
• Screenshare content is always downscaled to improve performance, but extensions receive more downscaling due to 50 MB memory limit. Previously, app screenshare was not downscaled from 1920 width and might have very low frame rate
• The screen track is always published in high priority

Also, subscriber / viewer functionality has been added

• Connect with bandwidth profile in presentation mode
• Publish audio
• Publish thumbnail video from camera at low priority
• Screen content is given the highest priority / bandwidth / size on screen
• Pinch to zoom and tap to zoom screenshare video
• Tap to mute or long press to mute / disconnect

TODO

• [x] Make extension audio optional
• [x] Bump Podfile and Cartfile
• [x] Sizing of viewer button
• [x] Try H.264 screencast at higher FPS
• [x] Finish adjusting scaling & bitrate for each use case
• [x] Publish thumbnail video
• [x] Show video thumbnails of local/remote viewers
• [x] Tap to mute local audio
• [x] Tap to disconnect the Viewer from the Room
• [x] Fix scroll view zooming
• [x] Show the mute state
• [x] Update the mute state
• [x] Track switch-off events
• [x] Update README.md
• [ ] Add final screenshots of the app
• [ ] Make sure retransmissions are using the scaler path

Contributing to Twilio

All third-party contributors acknowledge that any contributions they provide will be made under the same open-source license that the open-source project is provided under.

• [x] I acknowledge that all my contributions will be made under the project's license.

[ceaglest]

I have noticed that there are some layout issues on the iPhone X related to insets on the collection view, and zooming the scroll view. It might need a little more effort to fix, but this PR is ready for a look.

[ceaglest]

Screen recording of the app UI showing most of the new features:

RPReplay_Final1591925997.MP4.zip

[ceaglest]

What do you think about showing two buttons in home page : Presenter, Viewer. When user clicks on presenter - we give them option to use In-App Vs extension ?

I like that, it would be a lot cleaner than 3 large buttons. Otherwise we should just use a TableView with each option.

Do you think it is worth adding Viewer code in the sample app? Maintaining the UI will be painful. We can refer to the VideoApp if needed.

I think we should add a viewer UI. It offers the ability to pinch, zoom and scroll and demonstrates how to use bandwidth profile + publish for this use case. Not having a viewer experience is a source of confusion for the example app and the default QS does a bad job in this role.

[ceaglest]

Closing this PR since 4.0 has dedicated classes for ReplayKit functionality. The example will be updated to use the SDK APIs to access ReplayKit.