Time compression.

[artbatista]

Is there a way to do time compression on a video?

What I need is to take a video that is, let's say 30 minutes long and make it play in less time (say 28 minutes) without altering the sound pitch.

TV networks do it all the time, but I seem to come up blank for a way to do this.


Art

[adam]

Framerate (playback speed) is defined by your regional format. Ntsc uses 29.97fps and pal usees 25fps. These speeds are non-negotiable.

So the only way to shorten playtime and still have it playback on a television is to physically remove parts of the movie. This is exactly what networks do when they edit movies to fit a particular time slot. You need to get an mpg editor and remove parts here and there to make it fit the desired playtime.

[mbellot]

adam,

what artbatista is talking about is intentionally dropping individual frames from the video (and audio) stream at a low but useful rate to shorten the actual running time of a program without altering the actual contents.

For example, if you could drop 1 frame for every 60 you would effectively lose 1 second in a 1 minute clip, while reducing your effective framerate by only 0.5fps.

30fps x 60 seconds = 1800 frames

1800 frames / 60 (1 in N drop) = 30 frames dropped

so the final mpeg would only have 1770 frames and therefor only be 59 seconds long.

I realize the actual framerate is 29.97fps, but 30 made the numbers simpler.

Broadcast TV does this all the time, because it lets them sell extra commercials. Using my 1 in 60 example you get 30 seconds "freed up" in a 30 minute program.

Unfortunately for artbatista, I have never seen anything like this for the PC video enthusiast.

[artbatista]

adam,

what artbatista is talking about is intentionally dropping individual frames from the video (and audio) stream at a low but useful rate to shorten the actual running time of a program without altering the actual contents.

For example, if you could drop 1 frame for every 60 you would effectively lose 1 second in a 1 minute clip, while reducing your effective framerate by only 0.5fps.

30fps x 60 seconds = 1800 frames

1800 frames / 60 (1 in N drop) = 30 frames dropped

so the final mpeg would only have 1770 frames and therefor only be 59 seconds long.

I realize the actual framerate is 29.97fps, but 30 made the numbers simpler.

Broadcast TV does this all the time, because it lets them sell extra commercials. Using my 1 in 60 example you get 30 seconds "freed up" in a 30 minute program.

Unfortunately for artbatista, I have never seen anything like this for the PC video enthusiast.

That's exactly what I am talking about. I actually found a program from Apple that does just that. It "loses" frames here and there where the program thinks it won't be noticed, and it also speeds up the audio play to match the video, while adjusting the pitch to make it sound normal.

The end result is that it encodes let's say a 1 hour video to as little as 54 minutes (more than 10% time compression is not recommended), it speeds up the sound to match, it lowers the pitch of the sound to match the original sample, etc.

Unfortunately it runs only on the latest Mac hardware, PC's need not apply, and it is also quite pricey.

Here is a link for anyone interested.

http://store.apple.com/1-800-MY-APPLE/WebObjects/AppleStore?productLearnMore=M8562Z/A

Art

[EricB]

With Premiere, you can set the duration of a file so you could take a 30 minute video and change the length to 28 minutes. I doubt that you would see or hear much difference in the video or audio.