This project uses the custom video driver features in the OpenTok iOS SDK. By the end of a code review, you should have a basic understanding of the internals of the video capture and render API, as well as how to start building your own extensions to the core OTPublisherKit and OTSubscriberKit classes.
Note that this sample application is not supported in the XCode iOS Simulator because the custom video capturer needs to acquire video from an iOS device camera.
For our example, we create the TBExamplePublisher and TBExampleSubscriber classes. Like the OTPublisher and OTSubscriber classes, these are subclasses of the core OTPublisherKit and OTSubscriberKit classes, and they provide implementations for the video capture and render interfaces, where needed.
TBExamplePublisher binds the device's camera to the core publisher class, OTPublisherKit. The enabling mechanisms behind the scenes are a driver to interface with AVFoundation (to manage the camera and provide video), and the OTVideoCapture interface, which allows us to source arbitrary video data into the OTPublisherKit runtime.
###TBExampleVideoRender
Both TBExampleSubscriber and TBExamplePublisher need an instance supporting the
OTVideoRender protocol to display video contents. In short, the instance
ID that is set to the videoRender property will receive YUV frames (I420) as
they are captured (publisher) or as they are received (subscriber). Note that,
although the publisher's OTVideoCapture interface can process multiple pixel
formats, the images passed through the rendering callback will always be in the
I420 YUV format.
TBExampleVideoRender is a copy of the default video renderer for the OpenTok iOS SDK. It is borrowed and modified from a series of classes in Google's WebRTC project.
In this example we wire a video renderer to the publisher's rendering
callback. An alternative approach for developers using video from the camera
with AVFoundation is to wire AVCaptureVideoPreviewLayer directly to the
capture class and leave the OTPublisherKit.videoRender property nil.
To see TBExampleVideoRender in action, put a breakpoint on renderVideoFrame:.
You will see this method called for every video frame that is presented to the
rendering endpoint by the OpenTok iOS SDK.
###TBExampleVideoCapture
This class interfaces with AVFoundation to provide video capture support from the device's camera hardware. By implementing the OTVideoCapture interface, it can be used as a video capture endpoint TBExamplePublisher to provide video for publishing.
To see TBExampleVideoCapture in action, put a breakpoint on
captureOutput:didOutputSampleBuffer:fromConnection:. This method is invoked by
AVFoundation for every frame that is output from the camera capture session.
After some processing, the video capture invokes its own
OTVideoCaptureConsumer with the captured frame. Note the consumer is set by
the OpenTok iOS SDK during instantiation of the publisher.
The ViewController for this application is a near-identical clone of the previous, with text substitutions for our newly-minted example publisher and subscriber classes. Notice how a majority of the calls made into the OpenTok iOS SDK classes are declared on the core classes, OTPublisherKit and OTSubscriberKit. Extending those core classes as is done in this example is as simple as defining a few simple interfaces and plugging everything in at runtime. We hope that this new class hierarchy will give you some ideas for how to extend the core functionality of the OpenTok iOS SDK to meet your application needs.