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Old 07-15-2020, 11:59 AM   #1
Phazma
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Default Incorrect frame shown when placing edit cursor + playback start lag

Why is timeline-frame synchronisation inaccurate and why does video playback lag / jump frames on playback start or when seeking during playback?
When I want to synchronise the impact of a sound with an action in the video I always need to place the edit cursor few seconds before the frame of contact and advance with a hotkey action frame by frame until I reach the right frame to be sure that the still image on the video player portrays the frame of contact at the right point in time and I can place the audio transient correctly.

And when checking playback I also need to place the edit cursor a few seconds in advance of the part I want to check because usually the first few frames are not displayed correctly - the display is fixed at some random frame (as explained before) and when starting playback it remains at this frame or jumps shortly to another random frame and few seconds (or milliseconds) into playback it recovers and playback runs smoothly.

I don't know if I explained this well and if others have this problem too or it is just on my end.. but is it possible to fix this so that when I place the cursor somewhere in the timeline the correct frame is reliably shown and when starting playback the video starts immediately and exactly at that frame and not do some random flicker? I want to be able to trigger both video and audio exactly on hit/transient (or very shortly before) and see whether the impact works correctly, without those previously mentioned workarounds. It just feels a bit fiddly working with the video engine.

Last edited by Phazma; 01-05-2021 at 04:46 PM.
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Old 07-16-2020, 12:18 PM   #2
Eliseat
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I guess the problem is that Reaper doesn't support gpu in video editing. So every thing is computed with software and cpu which isn't nearly as efficient as using all the benefits of graphic cards video acceleration.

Your problem is well known. At least I can understand that synchronizing sounds to video appears like guessing in some cases. What could help is to set the project settings to very low requirements (while editing) or even better, creating a proxy video with less resolution and but same frame rate (to stay in sync). Somewhere in the forum someone posted a script for creating proxy videos on the fly, but I never found a way to implement it. That's really a bummer because this could make things much easier.

I once made a video and put action sounds like explosions and shots to make it funny. And it also was very difficult to accomplish.

Hope this helps a bit.

Reaper devs! We need more video love!

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Old 07-16-2020, 11:55 PM   #3
Phazma
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Okay thanks for clarifying and for the advise on proxy videos (going to try).
It's a pity that Reaper doesn't handle this better but at least now I know that it is not an error on my side and I am not making my life more difficult than needed.
I am used to working like this anyway so I will just keep doing so, hoping that Reaper will eventually fix this in an update.

Btw for those who need to do such synchronisation work I recommend the scripts "spk_Move edit cursor forward(/back) by 1 frame". I mapped these to the left and right arrow keys and just place my edit cursor somewhere that I am sure that the frame has yet to come and then advance frame by frame with the action until reaching the contact frame. With this method it seems that the frames are shown correctly and when checking how it plays back (from enough seconds earlier) it feels accurate.
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Old 01-05-2021, 07:08 PM   #4
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Ah, yeah, fixing some of this!
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Old 01-06-2021, 12:21 AM   #5
Phazma
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Quote:
Originally Posted by Justin View Post
Ah, yeah, fixing some of this!
Great, thanks! Super curious how it will work after the fix
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Old 01-06-2021, 01:02 AM   #6
GeneralMidi
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GPU support?
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Old 01-06-2021, 02:46 PM   #7
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Just some bugs fixed! Try the latest +dev build (pre-release forum), if you like!
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Old 01-08-2021, 09:40 AM   #8
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@Phazma, may I ask what kind of encoding you are using for your videos?
I'm doing this for quite some time now in Reaper and never had the issue, that frames don't show correctly.

It was quite an odyssey for me to find the right video format (for DAWs in general, not Reaper in particular), but what you would want in general is a video that encodes EVERY frame separetly, that means, the video shouldn't use B or P-Frames, because those need to be calculated depending on the previous / next frames. That's why I always request videos from editors that have every frame encoded indepedently.

Anyway, sorry for stating the obvious if you are already following all these things. But just checking!
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