Turns one H.264 sample from MP4's length-prefixed NAL units into Annex B: a start code before each NAL unit, the
track's parameter sets before an IDR frame that carries none of its own, and an access unit delimiter after the
frame, so a decoder reading a stream closes the frame without waiting for the next one. null when a length prefix
runs past the sample.
Turns one H.264 sample from MP4's length-prefixed NAL units into Annex B: a start code before each NAL unit, the track's parameter sets before an IDR frame that carries none of its own, and an access unit delimiter after the frame, so a decoder reading a stream closes the frame without waiting for the next one.
nullwhen a length prefix runs past the sample.