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Old 06-03-2023, 01:03 PM   #1
EricTbone
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Default Black frames between video clips on render

Reaper is rendering black frames between video clips.

Doesn't matter if the clips are snapped to each other exactly (on frame boundaries) or overlapping. It's the transition from one media source to another that causes the issue.



This occurs regardless of render settings -- renderer (WMF, FFMPEG), format (e.g. MPEG2, H.264, GIF), resolution, framerate, bitrate, offline/online rendering, so on and so forth.

There is a major pause during rendering when Reaper encounters the next video clip. It's at these points that the black frames in the output occur.

Here's what that looks like during rendering.

The black frames are not visible in Reaper during editing. If you overlap clips and use "item fades affect video", you can step through each crossfade in Reaper, frame by frame, and every frame looks exactly as it should. However, when you render, there are several black frames at the start of every crossfade (clip transition).

The source clips were rendered by Reaper without issue. Here are item properties as shown by Reaper:

Video: 3840x2160@29.97fps, Aspect=1.00, Decoding format=I420/YV12
Audio: 44100Hz 2ch 32bps
Video: h264 (High) (avc1 / 0x31637661), yuv420p, 3840x2160 [SAR 1:1 DAR 16:9], 265136 kb/s
Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 256 kb/s

The source clips are 1-2 GB each and the media items are heavily offset into those clips.

I tried moving the source clips to a very fast SSD and there was no change.

Interestingly, I tried it with much shorter clips (<50 MB) -- intending to upload here as a reproduction case -- the problem went away. The clips are in the exact same format, just much shorter.

You see the same pause during rendering (see above) when it reaches a new clip, but it's shorter if the source media is smaller/shorter.

It tried introducing one of the larger files back into the timeline, in between the shorter clips. Transitioning between short clips produces no black frames, but transitioning to the large file produces black frames.

Googling "reaper video black frames", I found a report of a similar issue that was resolve by removing a background process, something totally separate and unrelated to Reaper.

That makes me think that maybe it's a performance issue, where if Reaper takes too long to get the data for the next frame, instead of waiting indefinitely... it just drops the frame. I dunno.

Last edited by EricTbone; 06-03-2023 at 02:37 PM.
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Old 06-04-2023, 07:30 AM   #2
Justin
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Which decoder mode is it using? Could try a diff mode and see if that helps.

IIRC the rendering will wait forever for frames to seek, but I’ll doublecheck that to see if there’s some timeout.
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Old 06-04-2023, 11:42 AM   #3
EricTbone
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Quote:
Originally Posted by Justin View Post
Which decoder mode is it using? Could try a diff mode and see if that helps.
Was decoding with FFMPEG. I just installed VLC and switched to that and... problem gone!

So happy and relieved that I can stop investigating other video editors. It's shocking how bloated other tools are compared to Reaper.
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Old 06-04-2023, 12:25 PM   #4
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If you're by chance crossfading videos with different formats (sizes) on Windows, check this:
https://forum.cockos.com/showthread.php?t=177702

edit:
Missed your previous post that you have it solved already.
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Old 06-04-2023, 12:56 PM   #5
EricTbone
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Quote:
Originally Posted by nofish View Post
If you're by chance crossfading videos with different formats (sizes) on Windows, check this:
https://forum.cockos.com/showthread.php?t=177702
Yup, that's one of many threads I found during my extensive googling. Tried that a few days ago.

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Originally Posted by nofish View Post
you have it solved already.
And very relieved! The editing experience is so much better than virtually any other NLE, never mind the ability to script actions.
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Old 06-07-2023, 06:47 AM   #6
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Quote:
Originally Posted by Justin View Post
Which decoder mode is it using? Could try a diff mode and see if that helps.

IIRC the rendering will wait forever for frames to seek, but I’ll doublecheck that to see if there’s some timeout.

Ah -- the timeout is 5s. We'll change that to something higher.
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