Flickering in 3D play functionality

[alessandrocennamo]

Actions before raising this issue

• I searched the existing issues and did not find anything similar.
• I read/searched the docs

Steps to Reproduce

The issue arise while in annotation-view for 3d tasks.
The issue happens on a self-hosted CVAT instance.
ISSUE:
When clicking on the play button, a gray screen is shown to indicate that a frame is getting loaded.
The time spent on a frame is smaller than the time on the gray screen.
This makes the video functionality unusable.

See video.

cvat_video3.mp4

Expected Behavior

No response

Possible Solution

A good fix could be to just avoid showing the gray screen in between frames (and hold the previous frame instead).
This will make the video functionality usable, even in case of very long loading time (will just result in a slower frames-per-second).

When navigating between frames with the next/previous buttons though I think it would be better to maintain the loading gray screen to distinguish between a frame and the next (in a video sequence they will be very similar).

Context

This issue affect the ability to review the annotation, as reviewers need to navigate through the video.
In addition, without the play functionality, it would not be possible to review that the labels are smooth in time (across different frames)

Environment

• ubuntu 20.04
• CVAT v2.23.1