Currently, a fragment's unit array is constantly reallocated during
splitting of a packet. This commit changes this: One can keep the units
array by distinguishing between the number of allocated and the number
of valid units in the units array.
The more units a packet is split into, the bigger the benefit.
So MPEG-2 benefits the most; for a video coming from an NTSC-DVD
(usually 32 units per frame) the average cost of cbs_insert_unit (for a
single unit) went down from 6717 decicycles to 450 decicycles (based
upon 10 runs with 4194304 runs each); if each packet consists of only
one unit, it went down from 2425 to 448; for a H.264 video where most
packets contain nine units, it went from 4431 to 450.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@googlemail.com>
This way, every CodedBitstreamType->split_fragment() function can
safely assume the fragment passed to them will be reference counted,
potentially simplifying code.
Reviewed-by: Mark Thompson <sw@jkqxz.net>
Signed-off-by: James Almer <jamrial@gmail.com>
This saves one malloc + memcpy per packet
The CodedBitstreamFragment buffer is padded to follow the requirements
of AVPacket.
Reviewed-by: jkqxz
Signed-off-by: James Almer <jamrial@gmail.com>
This makes it easier for users of the CBS API to get alloc/free right -
all subelements use the buffer API so that it's clear how to free them.
It also allows eliding some redundant copies: the packet -> fragment copy
disappears after this change if the input packet is refcounted, and more
codec-specific cases are now possible (but not included in this patch).
This is harmless and should not be a warning - unknown units are passed
through to the write functions unchanged, and no other code will interact
with them.
James Almer
Andreas Rheinhardt
Mark Thompson