This hack tries to pass as much information as possible from caps to the
decoder before it receives any buffer. These information can be used by
the OMX decoder to, for example, pre-allocate its internal buffers
before starting to decode and so reduce its initial latency.
This mechanism is currently supported by the zynqultrascaleplus decoder.
https://bugzilla.gnome.org/show_bug.cgi?id=792040
The OMX spec doesn't support HEVC but the OMX stack of the
zynqultrascaleplus adds it as a custom extension.
It uses the same API as the one of Android's OMX stack.
I used the H264 encoder code as a template.
https://bugzilla.gnome.org/show_bug.cgi?id=785434
This information can be useful to zynqultrascaleplus decoders. They may
use this information to reduce startup latency by configuring itself
before receiving the first frames.
We also have a custom OMX extension allowing the decoder to report the
latency. The profile/level information helps it reporting a more
accurate latency earlier.
https://bugzilla.gnome.org/show_bug.cgi?id=783114
