RE: MPEG-1 Codecs

A1Burokas@aol.com
Mon, 5 Oct 1998 17:57:26 EDT

In a message dated 10/5/98 5:49:22 PM, palf@netcom.com responded to:

> >1) do streams that have been altered (with fades and dissolves)
> > keep their original bitrate, or are you forced to raise the bitrate?

with:

> They keep their original bitrate.

To which I muse... about MPEG 1 & 2 and how they reduce the data rate by
only saving the changes between frames (taking natural keyframes for granted).
If you have a static scene, with someone alking, it will have data rate A.
If you add a cutaway to a product shot and cut back to the talking head, I
would think the data rate would jump at those two edit points, and thusly, the
overall data rate would increase a little bit.
If you go back and edit a dissolve to a product shot and dissolve back to
the person talking into that MPEG stream, I would believe that the data rate
would go up by a large extent- because the entire image is changing.
The only way you could maintain a given data rate while adding changes
that require additional data, would be to reduce the quality of the video
overall. IS that right?

Anthony
________
Anthony Burokas, Media Technician, IEBA Productions, Inc., Phila. PA
+ Digital Video Consulting and Integration + DV/ DVCAM Sales +
V: (215) 632-3283 + Fax: (215) 612-0663
Go to: <A HREF="http://ieba.com">IEBA.com</A> to find out more.

"Ok, so what's the speed of dark?"