Helpful Document on H264 Compression Bandwidth
In helping a user who was having jittery playback, I came a document from Adobe which might be useful to everyone here. Specifically, within you'll find a very useful formula to estimate what the optimum bandwidth for an H264 movie. (Note that this applies to H264 movies only. Apple Pro Res uses a completely different compression scheme, and so this formula doesn't apply.
Here's the link: http://www.adobe.com/content/dam/Adobe/en/devnet/video/articles/h264_primer/h264_primer.pdf
(Perhaps others disagree with the advice I'm about to give below; if you're experience tells you differently, please "chime in" to this discussion.)
If you go to page 22 of the Adobe PDF, you'll see they suggest a formula for calculating the optimum bit rate for an H264 movie. The formula works like this:pixels across * pixels down * frame rate * motion rank * 0.07Where motion rank is one of three values:
- Motion Rank 1 = Low motion is a video that has minimal movement. For example, a person talking in front of a camera without moving much while the camera itself and the background is not moving at all.
- Motion Rank 2 = Medium motion would be some degree of movement, but in a more predictable and orderly manner, which means some relatively slow camera and subject movements, but not many scene changes or cuts or sudden snap camera movements or zooms where the entire picture changes into something completely different instantaneously.
- Motion Rank 4 = High motion would be something like the most challenging action movie trailer, where not only the movements are fast and unpredictable but the scenes also change very rapidly.
Let's say that your video is motion rank 2. For a 1920 x 1080 video this means1920 x 1080 * 25 (fps) * 2 (motion rank) * 0.07 = 7257600 bits / second = 7087 kilo bits / second = 6.92 mega bits/second.The 1920 x 1080 videos I used to test Isadora are 10 Mbps, so that's pretty close to the suggestion above.
Since I think this is quite useful, I made an Isadora patch that does the math for you. Just enter the four factors (width, height, fps, motion rank) and it will tell you the optimum bandwidth.
Hopefully this will give us a benchmark from which we can discuss compression factors in the future.
All the Best,
Very interesting. Not too long ago I was asking CreativeCow community for this kind of information. There was no reply at all. And here we are - great find
Very interesting, thanx Mark!