I'm composing a 2D video from two different sources, with the final product being at 30 FPS.
One of the sources was recorded at true 30 FPS, and the video & audio streams have the same number of frames when I add the Movie/Sound strips.
The other source, however, is slightly off: the audio came in at 14,726 frames and the video 14,876 frames.
So I added a Speed Control effect attached to the video strip, and set the speed factor to 1.010 (14,876/14,726). When I preview the video in Blender, the audio and video are synced up perfectly and the video looks just like the source.
The problem is that when I render the video, it ends up containing visual artifacts like jitteryness and sometimes even speedups and repeats that aren't synchronized with the audio (sorry, this is hard to describe in words). The audio track itself is fine. I thought it might be a problem with the output format, so I tried a few different ones, and found this happens even if I render to a set of images (I simulated playback using Windows Photo Gallery).
The artifacts disappear if I remove the Speed Control effect, but of course, the video & audio are no longer in sync.
Am I doing something wrong here (I'm new to Blender)? Is there any alternate method to accomplish this? I need something that works reliably and efficiently as this isn't a one-time-only project.
(I also found there appears to be issues doing soft cutting with the Speed Control effect -- I may be misunderstanding how to do that -- so my goal at this point is to first convert the entire video source on its own, and then do all the cutting in the final step.)
I'm using Blender 2.68a. I tried using the latest dev build from today (same result), and also 2.57b, which not only had the rendering problem, but also didn't look right in the preview. I'm running Windows 7 x64. Here's the .blend file I'm using.
Here are sample renderings of part of the video: from 2.68a and from 2.57b (each file is ~4.5 MB) -- sorry I can't upload the source as the file is over a gig, but it should be obvious from those videos what's supposed to be happening (listen to the mouse clicks). Before someone asks, yes, this also happens when I render the full video (in fact, that's how I discovered it in the first place). I was able to reproduce problems in short sample clips as well, though not as severe as those two examples.