[Bug 796521] msdk: Playback not smooth by using ximagesink.

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=796521

--- Comment #9 from sreerenj <bsreerenj at gmail.com> ---
It is possible to get cached and un-cached memory in the output.

Libva allows two methods to map video memory,

Method_1: directly map with vaDervieImage (it is supported in iHD driver and
vaapi-intel-driver).
In usual use cases, the VASurface wrapping the tiled (Y-tiled) video memory and
the memory mapped using vaDeriveImage() API is tiled too. In this case, driver
uses the drm_intel_gem_bo_map_gtt() to map a tiled memory which generates  USWC
memory.

Method_2: Create a VAImage structure using vaCreateImae api and user-specific
video format. Then we download the vaSurface (which has decoded content) using
shaders or vpp by invoking vaGetImage() api.
This will generate "Linear" memory and this is Cacheable by CPU.


We chose the method 2 as default in GStreaemr-vaapi if there is a requirement
to map the video memory for software operations.

But gst-msdk only has support for method_1 and we stuck with USWC memory. The
iHD driver wasn't properly supporting the vaGetImage(), not sure about the
current status though.

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