v2: - cover letter - testing explanation - signed-off-by V4L2 supports hierarchical P frames via the V4L2_CID_MPEG_VIDEO_H264_HIERARCHICAL_CODING* controls. These controls are needed for implementing the L1T2 web standard[1]. L1T2 is a way to specify a bitstream that every other frame is unreferenced and therefore can be dropped without causing artifacts during playback. ChromeOS is planning to use this feature for video conferencing apps. A single encoded stream can be shared to clients with different performance characteristics. Those with lower bandwidth or slower decoders only need to receive the referenced frames, not the unreferenced ones. The changes in the patch have been run through the ChromeOS tast test system to verify no regressions are occurring on a SC7180 board. Hierarchical P frames are not yet integrated into the test system. These changes have instead been checked using a bitstream analyser to verify the reference frame management. [1]: https://www.w3.org/TR/webrtc-svc/#L1T2*
