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Old 03-23-2023, 10:58 AM   #1
Human being with feelings
Join Date: Jul 2005
Location: Boston
Posts: 22
Default High-Resolution & Low-Resolution Peaks Out Of Alignment On 59.94 FPS Video Files

Here is an example of the issue:

As you can see, when I zoom in past the threshold for low-resolution peaks, and the peaks switch to high-resolution peaks, the waveform jumps considerably

This misalignment happens to a much greater extent further into the video file: at the top it's not noticeable, but once we're an hour+ in, the alignment jumps considerably when switching to high-resolution

After some experimentation, I am 90% sure that what's going on is: the low-resolution peaks are running faster than the high-resolution peaks. I gather this, because when I scroll to the end of the video file, the low-resolution peaks appear to "run out", leaving a silent-looking gap at the end... where there is no silence. If I zoom in to high-resolution peaks, it still shows a (seemingly-accurate) waveform

This leads me to believe that the low-resolution peak files might have an incorrect timebase going on? Frame-rate? Sample-rate?

I've tried rebuilding the peaks; it doesn't fix it. Same thing happens

The file in question is a .mp4 with the following specs, according to Source Properties:

Length: 1:00:03.731
Video: 1280x720@59.94fps, Aspect=1.00, Decoding format=I420/YV12
Audio: 44100Hz 2ch 32bps

Using VLC decoder (v3.0.x) for video and audio

Video: h264
Audio: mp4a

Loaded from: /Applications/VLC.app
Note that the fps is listed as 59.94... maybe that explains this wackyness?

Regardless, it's incredibly frustrating; it's impossible to sample-align the audio if I have no idea where the samples actually are!

I'm not sure why this is happening with that video item and not the one on the track above it, but it's a thing I've seen happen before in REAPER when dealing with video items especially

I'm on 6.64 on OSX 12.5

Last edited by phNord; 03-23-2023 at 11:08 AM.
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Old 03-24-2023, 07:12 PM   #2
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Join Date: Jan 2005
Location: NYC
Posts: 15,213

On some video files with compressed audio the seeking isn’t 100% accurate with VLC decoding. You might want to try using AVFoundation for video decoding?
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