Emanuel
01-15-2006, 08:03 PM
The HDV format is highly compressed, right?
Here (http://www.showreel.org/memberarea/article.php?45), it says: «approximately, 27:1 for 720p and 47:1 for 1080i» or is it wrong?
And which are the numbers for the DVCPRO-HD at the different two resolutions?
Barry_Green
01-15-2006, 08:34 PM
HDV720p fits 27.6 megabytes into 19 megabits. HDV1080i fits 46.6 megabytes into 25 megabits. But it's not at a constant compression ratio. You can't just do the math and declare that it's such-and-such compression ratio, because it depends on the changes between the frames and how the frames in the group of pictures are all laid out. Over the course of a group or longer, yes it'll net out to a constant data rate, but the individual compression per frame can vary significantly depending on where the codec thinks it needs its bits to be allocated. If there's very little change between frames the compression can be very efficient; if there's a lot of change between frames the compression can become quite taxed. It's not constant.
DVCPRO-HD is a constant compression ration, it's always 6.7:1. Each frame is compressed discretely to an exact size, and it's always 6.7:1.