VA-API expects slice_vertical_position as the initial position from the
bitstream. i.e. the direct slice() information. VA drivers will be fixed
accordingly.
Unlike what VA-API documentation defines, the slice_data_bit_offset
represents the offset to the first macroblock in the slice data, minus
any emulation prevention bytes in the slice_header().
This fix copes with binary-only VA drivers that won't be fixed any
time soon. Besides, this aligns with the current FFmpeg behaviour
that was based on those proprietary drivers implementing the API
incorrectly.
Original values from sequence_header() are 12-bit and the remaining
2 most significant bits are coming from sequence_extension().
Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
6.3.15 says that "some slices may have the same slice_vertical_position,
since slices may start and finish anywhere". So, we can't submit the current
picture to the HW right away since subsequent slices would be missing.
vaRenderPicture() implicitly disposes VA buffers. Some VA drivers would
push the VA buffer object into a list of free buffers to be re-used. However,
reference pictures (and data) that was kept would explicitly release the VA
buffer object later on, thus possibly destroying a valid (re-used) object.
Besides, some other VA drivers don't support correctly the vaRenderPicture()
semantics for VA buffers disposal and would leak memory if there is no explicit
vaDestroyBuffer(). The temporary workaround is to explcitily destroy VA buffers
right after vaRenderPicture(). All VA drivers need to be aligned.
This ensures the VA context is clear when the encoded resolution
changes. i.e. make sure older picture is decoded with the older
VA context before it changes.
On sequence end, if the last decoded picture is not output for rendering,
then the proxy surface is not created. In this case, the original surface
must be released explicitly to the context.
VA drivers may have a faster means to transfer user buffers to GPU
buffers than using memcpy(). In particular, on Intel Gen graphics, we
can use pwrite(). This provides for faster upload of bitstream and can
help higher bitrates.
vaapi_create_buffer() helper function was also updated to allow for
un-mapped buffers and pre-initialized data for buffers.
Only the explicit pred_weight_table(), possibly with the inferred default
values, shall be required. e.g. don't fill in the table if weighted_pred_flag
is not set for P/SP slices.
Keep a valid reference to the proxy in GstVaapiPicture so that frames
marked as "used for reference" could be kept during the lifetime of the
picture. i.e. don't release them too soon as they could be re-used right
away.
