Posted: Sun, 7th Jun 2009, 3:03am
Post 1 of 4
I recently was watching a short video that i had added a few effects to with Visionlab and realized that a gun shot effect which I know i saw on the same video a few days before post-rendering had dissappeared. The effect then came and went a couple of times watching the video again and again. Has anyone else encountered this? I was under the impression that once the video was rendered out of the lab the effects were permanently attached. could anyone shed some light on this one for me? thanks for your time.
Posted: Sun, 7th Jun 2009, 4:30am
Post 2 of 4
Most likely the effect only lasts for a single field, or half of one frame, of your video which is interlaced. When it is played back on a progressive screen, only your computer, it will only appear if the playback software decides to use the field containing the effect for that particular frame.
In case you aren't familiar with the concept of interlacing, here's a quick explanation. Nearly all video cameras record interlaced footage, as nearly all video playback devices and televisions display in interlaced format. This means that NTSC footage, with runs at 30 frames per second (technically 29.97, but that's another story) doesn't display Frame 1, 2, 3, 4 etc., but rather, Frame 1a, 1b, 2a, 2b, 3a, 3b etc. Each field is displayed for 1/60th of a second, so fields 1a and 1b combine to last 1/30th of a second, or the duration of frame 1. Each field contains either the odd numbered or even numbered horizontal lines of resolution of the frame, and when played back in sequence, they are interlaced to create the entire frame.
Now, where things get confusing is that computer monitors aren't interlaced, they are progressive, so they will only display one or the other of the fields when you play back the footage. So if you have an effect that only appears on the even field, and the computer uses the odd field during playback, the effect won't appear. The best way to avoid this is to make sure any effect lasts an entire frame, or two fields, when working with interlaced footage.
Posted: Mon, 8th Jun 2009, 12:00pm
Post 3 of 4
You are right on the money axeman. It is a very quick effect. Thank you for the explanation. It makes alot more sense now, and gives me confidence in the program for the future as well. I don't suppose the human eye would really be able to discern if I lengthened the muzzle flash to extend to a full frame anyways huh? Thanks alot for your time!!
Posted: Mon, 8th Jun 2009, 3:02pm
Post 4 of 4
Nope, at a full frame, your computer will still only display one field or the other, and when played back on a tv, where you see both fields, it still only lasts a 30th of a second or so. It'll still be very very quick.