tree a9293bdfd6322cbca456e6a6029aaf6233ed8a89
parent 6b231dc136e4c1f2cb4ed923c19453f76adf843c
author Marco Paniconi <marpan@google.com> 1632863151 -0700
committer Marco Paniconi <marpan@google.com> 1632870786 -0700

rtc: Fix to lm=3 pattern in svc sample encoder

For the 3TL pattern with multiple references (lm=3):
fix the ALTREF ref_idx so that the ALTREF trails
the enhancement layer frames (in current code it
was only trailing on the TL0 frames), so TL2/TL1
frames can also use the ALTREF as a reference.

Also enable compound prediction for (LAST, ALTREF)
for speed >= 7 for pattern lm = 3.

For speed 7 on rtc _set for 3TL with lm = 3:
bdrate gain from altref ref_idx fix is ~1-2%,
bdrate gain from enabling compound prediction is ~5%.

Change-Id: Ia5def436e7c7c6a27cb74dfe33d231f862022cf0