Hi,

I can't find out what's causing rough playback. It's been an issue for a long time and it's always worse than it needs to be, regardless of the clip framerates and project settings (although a mismatch between clip, project and display Hz will always be an issue).

As a test, I created a 1080@30p prores .MOV, also set the kdenlive project to 30p and played the clip in the timeline. He're a representative screencapture: https://youtu.be/FyygMpqnjZQ?t=4
*the screencapture program does occasionally drop or add duplicate frames, but nothing approaching this amount.

Here's the same source clip converted to h.264 and uploaded straight to YouTube: https://www.youtube.com/watch?v=81PXHx1moEk
^This gives completely smooth playback with Firefox's HTML5 player.

Since 60Hz display refresh divides cleanly to 30p, kdenlive (or Xorg) should just repeat each frame twice. From stepping through the screencapture video in slow motion, the frame sequence is something like this:
1,1,2,3,3,4,4,4,5,6,6,8,8,8,8,9,9 (some frames are missing entirely)

ffplay stutters occasionally, but not as frequently as kdenlive.

mplayer stutters quite a bit, and it might be in some way related to the lack of vblank/sync with my nvidia card - the video starts playing smoothly, then a familiar vblank shearing line will move slowly up the screen and everything below it will be stuttering. when the shearing line hits the top of the screen, another line starts again at the bottom and everything underneath is smooth. this pattern seems to repeat. (hope that makes sense)

System details:
Suse Leap 42.1
Kdenlive 15.12.3
Xfce 4.12

please try to update to the latest version 16.08 and let us know if this still happens... there is now a new feature to change the preview quality of compositing to speed up the timeline as well as a new render of timeline effects.


cheers

farid wrote:please try to update to the latest version 16.08 and let us know if this still happens... there is now a new feature to change the preview quality of compositing to speed up the timeline as well as a new render of timeline effects.

Hi,
Unfortunately my distro only has 15.12.3 and I'd prefer not to switch repositories - doing so has caused problems in the past with libraries getting out of step.

I'm not doing any compositing or using effects - it's just a clip in the timeline, so would there be any improvement in that case?

Firefox no longer seems to play back the 1080p clip smoothly, although that might be partly caused by number of windows and tabs I've got open...

There's definitely something strange going on with vsyncing and X. I've since noticed ffplay has a similar tearing/juddering issue as mplayer. Unfortunately the 'vblank' option on the nvidia driver panel only seems to work with GL applications (and even then people have reported problems). Since ffplay doesn't use GL to draw to the display (to my knowledge), I can't see it would help.

I might try and ask over in mplayer/ffmpeg channels as it might point to a similar root issue.

Is it the case the kdenlive doesn't use OpenGL to draw the video preview?

EDIT: and does kdenlive have any sort of video buffer to store frames after they've been decoded but prior to display? Or is it designed so frames are decoded just-in-time (which could mean playback would be vulnerable to any spikes in system resources (I/O, CPU, etc)?