I have been using the option in preferences: File I/O ->Enable experimental HEVC decoding. I noticed recently whilst rendering a series of clips (11 clips = 8min 26sec) that at about 46% into the render it slowed down substantially. Using a series of tests I narrowed down the problem to one of the clips. The clip was only 9sec and 13frames (238frames), but the render time increased by a factor of about x120. I tried rendering with and without that option as well as using AMD 9070 acceleration, Radeon Graphics acceleration and not acceleration (CPU) and found they all suffered the same. Below are the statistics for rendering that clip, with and without the use of that setting:
GoPro12 4K (HEVC) clip - Gx010011.mp4 (9s+13frame = 238frames)
- Without using experimental HEVC decoding: Renders in 1.82s = 130.5 fps
- Using experimental HEVC decoding: Renders in 3min 42s = 1.07 fps
The rendered video results
- Without using experimental HEVC decoding: Video is 33.2MB and looks the same as source
- Using experimental HEVC decoding: Video is 19.4MB and flickers
Attached are the source video clips and the two rendered clips.