Originally Posted by 42041
I'm curious, how are digital intermediates and old HD masters stored? Is it a lossless (or close to it) format?
You can keep the lossless file you get from the scanner, but it will take about 50MB per frame in a 4K sample (More than 7TB for 100 minutes). Some do keep this.
You usually backup in the same format used for mastering, Apple ProRes 4:2:2 or Cineform 12-bit 4:4:4 raw for instance, an average of 250Mb/s. You can also get DVCPRO HD 4:2:2 around 100Mb/s, quite common when the source is a digital camera. And, in this last case (DVCPRO HD), a H.264 4.1 High Profile (8-bit 4:2:0 subsampled) transfer from this source, with an average bit rate of about 25Mb/s, should be more than enough.
I don't know what you mean by OLD, but tape was (and you can say still is...) a way to go.
About the frames, I frames are the base used by the B frames around it. A B-frame (compressed frame) does not necessarily means worse quality (You also have to consider the decoder and the specific frame), B-Frames are actually the compression per se (or a considerable part of it), the more B-frames more quality per Mb can be fit, the more I-frames (Full picture data) you decide to use the less compressed the video will be (In a way, better say "will be able to be"...) but since the B-frames will have more reference with more I-Frames, the motion will/should look better.
The B-frame holds only part of the data necessary to construct the whole frame, the rest is captured from the near I-Frames around used as references. Suppose you have a stationary background, you don't need to repeat all the data for the background in the B-frame, you can just reference it to an I-Frame next to it and before it. And that is what B-Frame stands for, Bi-predictive frame. H.264 also allows you to use a previous decoded B-Frame as a reference frame.
I suggest you guys visit http://forum.doom9.org/
lots of useful tech info about all this there.
The compression and ecoding follow many parameters, like motion estimation, the kind of B-Frames, the reference method, the entropy, decoding intensity, time and money...
In the end, bit rate does not mean much, you have to check the parameters not the Bit Rate. You may get the same quality with a lower bit rate, or you can waste bandwidth to facilitate decoding (Less compression). Pirates can often teach you a think or two about this bit rate thing...