EDIT: 2.77 includes this new feature: “Strips - Importing new movie strips now uses movieclip framerate”
So, maybe this trick is not usefull any more (I’m just downloading 2.77 right now, I’ve never try it)
As a suggestion, the source movies have to be the same framerate as the final framerate. But, if we have different framerate movies, we have to do some tricks…
First, we select the final framerate, for example: 29.97 (29,97002997). Then, we import the movies. If the movie framerate is, for example, 30fps, you have to:
- Select the movie track.
- Add “Effect Strip” - “Speed Control”.
- Make sure that “Use as speed” is checked and change the Speed Factor. In this case, the movie is 30fps and the final will be 29.97. So:
Source framerate / Final framerate = Speed factor
30 / 29,97002997 = 1.001 (check http://en.wikipedia.org/wiki/NTSC)
- “Speed Factor” would be 1.001.
Now, the movie speed is fine. If the movie has no audio, it’s done. But, if it has, we have to change audio speed. We won’t do it with “Speed Control”, but with “Pitch” option, in audio properties (I think it should be named “Speed” or “Time stretching with Pitch”). We change to 1.001, too.
If the movies framerates (source and final) are different, we have to calculate. E.g.:
24 / 30 = 0.8
15 / 30 = 0.5
30 / 24 = 1.25
30 / 15 = 2
24 / 29.97 = 0.8008008008… (*)
(*) Blender stores values with 6 decimals in Speed factor. If you input 0.8008008008 (10 decimals), you will see 0.801. But, internally, it is 0.800801 (6 decimals). I didn’t test it, but I think it is far enough.
There is another way to do it: uncheck “Use as speed” and enter keyframes at start and end. The first, has to be 0 (or 1) and, the last, a “calculated last keyframe”:
Source total lenght: 2880 (2 minutes at 24fps).
So… 29.97 * 2800 / 24 = 3596.4 (Cross-multiplication)
Final total lenght: 3596.4.
WHEN CHANGING TRIM DURATION OPTIONS
But, be carefull using keyframes with Speed Control… because, if you change source movie Trim Durations (soft or hard) to change the start of the movie, the Speed Control moves itself automatically to the start of movie… and, in this move, the keyframes do the same. You will have move keyframes by hand.