I've put the correct frame-rate to sync the audio & video, but the video still "lags"

Hello everyone.

I’ve been watching tutorials about Blender and noticed that they stressed on the frame rate issue, and as such I put in the correct frame rate. However, when I play the video it is still “lagging”. Here is what I did:

(picture attached for clarification)

I first opened the video with VLC to view its properties, showing that its frame-rate is 24.049760. I tried to put that into Blender but it only comes back with whole numbers, and in this case 24, so I left it 24 and imported the video. But the audio and video files were not in sync. The audio’s frame length was 647, whereas the videos frame length was 809.

So finally I went to the frame-rate base, changing it from 1.000 to .8. That did make the frame length of the files the same, but it changed the frame-rate into 30. I tried several times and I come up with the same result. So fingers crossed I played the video, yet it was “still lagging”.
I closed and opened blender again and imported the video. This time choosing different frame-rates. Suprisngly, when I chose a frame-rate of 30, the audio and video files were in sync even though the details of the video (via VLC) say its frame-rate is 24.049760. However, even so, when I played the video it was still “lagging”.

What seems to be the problem? Thank you


What camera did you use, that’s a weird frame rate, when I’ve seen it like that it’s usually been shot on an iphone or something like that and has a variable frame rate which is never good for any NLE’s not just blender.

If it were me I’d convert the footage to a standard frame rate first so in this case probably 24 fps or 23.976 depending on where you were going to publish it. I’d do that by dropping frames, you’ll never notice visually (unless it’s something like variable frame interlaced then you would have to sort that out first). Have a read up on https://ffmpeg.org/ if you want to keep it free or http://www.virtualdub.org/ which is probably a little more friendly. you may need to dig around for codecs etc. depending on how it’s encoded.

For the output format chose something that is NLE friendly and won’t add another round of compression to what will already be compressed video then you can just proxy that in blender if the performance sucks.

Suspect it’s what you are putting into blender rather than blender that’s the problem but as always could be wrong :slight_smile:

Thank you Umii for your help. I am currently looking into virtualub and ffmpeg to convert the frame-rate.

For all purposes, I’m using a Logitech C920 Camera with the following settings


Thank you

There are some additional setting in the advanced tab that may be causing your frame rate to drop, it should be running at 30 fps I think (perhaps 25 if you are in PAL region) see this vid near the end I’d try making sure everything is off like he says and do some test recordings I think you may be actually dropping frames rather than it being an actual deliberate variable frame rate he even mentions the audio going out of sync because of it. Probably spending some time testing it to see if you can get it constant if you are going to be doing it a lot to save fiddling about post processing, much better to capture it right if you can. You still might need to proxy it in blender depending on how compressed it is and the specification of your PC but if you can get a constant frame rate your audio should stay in sync.

Yes, ffmpeg is key, virtualdub is a bit outdated (last release in 2013). Only “downside” is ffmpeg doesn’t have a dedicated gui (at least on Linux). You can google “ffmpeg gui” for some options. But command line ffmpeg is so powerful once you figure it out.

I’d say convert your files to 24 fps and perhaps even an intermediate intraframe-only format like mjpeg or prores. These take up a lot of space but make editing and playback within Blender much more crisp. Or, just import the framerate-corrected video directly into Blender, but I’m not sure how accurate the cuts will be. I also run an older machine that tends to studder when using non-intermediate formats like h264.

For some info on intermediate formats: http://wolfcrow.com/blog/intra-frame-vs-inter-frame-compression/