4K playback optimization help needed

[QwjN1Y9mJvamZJ]

I would like to ask for some advice regarding how to make 4K playback
smoother. I don't think the issue is that my PC can't keep up with decoding,
because if I use /sync = false/ on the video sink, the video plays fast and
very smooth. Details follow:

1. The basic pipeline I tried:

/gst-launch-1.0.exe filesrc location=4K.mkv ! matroskademux ! h265parse !
nvh265dec ! glimagesink/

This works, but the image is a bit "choppy", as in I feel I can see as the
movie proceeds from one frame onto the next, especially when the camera is
panning. Initially I assumed that the jumpiness was because of the
discrepancy between the movie's frame rate (23.967) and that of my monitor
(60), but the file plays back perfectly smooth with a video player (Windows
10 x64, MPC-BE with LAV filters using CUVID hwaccel and EVR renderer). I
don't think that MPC-BE is using motion interpolation either.

As to why I'm using these filters: d3d11 filters (d3d11h265dec ->
glimagesink or d3d11videosink) only produce a white or gray image (perhaps
because the source is 10bit), avdec_h265 CPU processing is too slow, so all
I have left is the nvcodec filters, plus I don't know any memory:GLMemory
capable video sink other than glimagesink (glimagesinkelement didn't work,
not sure why).

2. sync=false

/gst-launch-1.0.exe filesrc location=4K.mkv ! matroskademux ! h265parse !
nvh265dec ! glimagesink sync=false/

Plays back the video at high speed. Really smooth and fast, so I suspect
it's not a performance issue I'm having. I've also tried to resizing the
video stream (using gltransformation) to 2K, after the nvh265dec, that
didn't change anything either.

Here are the things I've tried to improve the situation:

3. vsync=true

/gst-launch-1.0.exe filesrc location=4K.mkv ! matroskademux ! h265parse !
nvh265dec ! glimagesink sync=true vsync=true/

Not much changed, still small jumps from frame to frame.

4. videorate

/gst-launch-1.0.exe filesrc location=4K.mkv ! matroskademux ! h265parse !
nvh265dec ! queue ! videorate ! video/x-raw(ANY), framerate=60/1 !
glimagesink sync=true vsync=true/

Or video/x-raw(memory:GLMemory) caps. This "feels" a bit better, smoother,
but not perfect.

5. videorate + sync off

/gst-launch-1.0.exe filesrc location=4K.mkv ! matroskademux ! h265parse !
nvh265dec ! queue ! videorate ! video/x-raw(ANY), framerate=60/1 !
glimagesink sync=false vsync=true/

I've seen another thread ( Choppy prores 4K playback
<http://gstreamer-devel.966125.n4.nabble.com/Choppy-prores-4k-playback-td4691115.html> 
) in which it's mentioned that perhaps the individual buffers aren't
processed fast enough at the sink - not sure if it applies to my case, but I
assumed the above pipeline would avoid the problem of buffers being dropped
because they were displayed too slowly... even if that's not correct, so far
this has produced the best result, but it's still not as smooth as playing
it back with MPC-BE.

I've been able to get so far with gst-launch, I'm thinking maybe I could get
more information about what's really going on with programming this pipeline
in C, but I'd be happy if someone wiser could give me some ideas as to which
direction I should be going from here on.



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