VideoFrame

Java version of webrtc::VideoFrame and webrtc::VideoFrameBuffer. A difference from the C++ version is that no explicit tag is used, and clients are expected to use 'instanceof' to find the right subclass of the buffer. This allows clients to create custom VideoFrame.Buffer in arbitrary format in their custom VideoSources, and then cast it back to the correct subclass in their custom VideoSinks. All implementations must also implement the toI420() function, converting from the underlying representation if necessary. I420 is the most widely accepted format and serves as a fallback for video sinks that can only handle I420, e.g. the internal WebRTC software encoders.