When sample batching is disabled, copying of the ByteBuffer data
is not necessary as samples are written as they arrive.
Copying of the BufferInfo is necessary because the info is needed
for writing the moov atom.
The input ByteBuffer can be in little endian order, or have its
position set. AnnexBUtils now ensures big endian order before
inspecting bytes, and supports reading from a non-zero position.
This change reduces the amount of memory allocations by Mp4Muxer
in its default configuration
PiperOrigin-RevId: 723401822
f8f66bdfaa