Normally, this function tries to make sure all threads are saturated with
work to do before returning any frames; and will continue requesting packets
until that is the case.
However, this significantly slows down initial decoding latency when only
requesting a single frame (to e.g. configure the filter graph), and also
wastes a lot of unnecessary memory in the event that the user does not intend
to decode more frames until later.
By introducing a new `flags` paramater and a new flag
`AV_CODEC_RECEIVE_FRAME_FLAG_SYNCHRONOUS` to go along with it, we can allow
users to temporarily bypass this logic.
Reorganize the code such that the frame threading code does not call the
decoders directly, but instead calls back into the generic decoding
code. This avoids duplicating the logic that wraps the decoder
invocation and allows receive_frame()-based decoders to use frame
threading.
Further work by Timo Rothenpieler <timo@rothenpieler.org>.
thread.h currently contains both API for decoder use and functions
internal to lavc generic layer. Move the latter to avcodec_internal.h,
which is a more appropriate place for them.
The goal is to distinguish between APIs provided by the generic layer to
individual codecs and APIs internal to the generic layer.
Start by moving ff_{decode,encode}_receive_frame() and
ff_{decode,encode}_preinit() into this new header, as those functions
are called from generic code and should not be visible to individual
codecs.
