The new reader is named H263Reader as it handles H.263 streams, but MPEG-4 Part 2 streams are also intended to be handled. The reader's output format MIME type is video/mp4v as the H.263 streams can be decoded by decoders supporting this MIME type. The implementation is based on the framework implementation for extracting MPEG-4 video in MPEG-TS (https://cs.android.com/android/platform/superproject/+/master:frameworks/av/media/libstagefright/mpeg2ts/ESQueue.cpp;l=1825;drc=86e363c1fac27302ca4ae33e73296f7797672995) and is similar to the existing H262Reader. Issue: #1603 Issue: #5107 PiperOrigin-RevId: 320565337
