and that is the ONLY frame rate that DVCProHD will touch the 100mb/s mark and that all others are lower....like for instance, shooting DVCProHD @ 24p is more like 40mb/s no matter what??

If that's true, then it seems you will be able to fit almost double the recording time on the new P2 cards, huh??

- Shannon W. Rawls

<<<-- Originally posted by Shannon Rawls : and that is the ONLY frame rate that DVCProHD will touch the 100mb/s mark and that all others are lower....like for instance, shooting DVCProHD @ 24p is more like 40mb/s no matter what??


When the Varicam records, it always records at 720/60P, this is 100Mbs. When you extract frames, you have what ever that fraction is, so when I extract 24P from those 60 frames I end up with 24/60th of the data or 40P

Hope that helps,

Jan

Okay, here's the deal, as I understand it: DVCPRO-HD records on tape at 100 megabits per second, regardless of anything. When recording 1080i, it records at 100 megabits. When recording 720p, it records at 100 megabits on tape.

Now, when recording 1080i, there are no other frame rates available -- it only runs at 60i (although, I guess they could implement 1080/24p or 1080/30p within a 60i data stream, like they incorporated 480/24p and 480/30p within a 60i data stream on DV). But I digress...

... because with 720p, there is the potential for recording varying frame rates (hence the name VariCam). However, the tape only runs at 100 megabits per second, always and ever. So if you're recording to tape, you'll be recording 100 megabits. But if you're using a different frame rate (such as 30p), the way it does it is to sample 30 frames per second, and add duplicate frames to pad out the data stream to 60p (which is 100 megabits).

When digitizing that footage from tape, you can use the Frame Rate Converter to strip out the duplicate data and end up with a smaller file on disk. For example, that 30p file would actually occupy a file size of 50 megabits per second, after the duplicate frame info is removed. Same with 24p: it would occupy a 40 mbps file size.

The tape must be 100 megabits. But P2 isn't tape, it's a file storage system like a hard disk.

So the question is, is there any reason that the camera couldn't record to P2 memory at the frame-rate-conversion size? It seems reasonable, and I hope there's no technical reason why they couldn't. If they can record only the individual, distinct frames (and discard the duplicate frames) then yes, it would seem reasonable to think that a 24p stream would take up 40 megabits of space. Which would give you 2.5 times as much storage space on the P2 cards!

I'm sure this is the way it will be implemented, unless there's some compatibility/technical reason that we don't know about...

It would be ludicrous to think, that on the p2 memory cards, that redundant repeat frames get recorded.

Graeme

So if rate is reduced by 2.5, means DVCPRO50 will be too, so we could record in this P2 around 10 min. of this format.

That sounds a lot better!Its not so big sacrifice to film in PRO50 ten minutes and drop it in the Hard Disk... Much, much better than Dv and Mpeg2!

I´m on it!

Well... depends on the size of the card. DVCPRO-HD runs at a maximum rate of 100 megabits, and like Graeme said, it would be silly to record the duplicate frames. I'm assuming there's no technical reason that they would need to be recorded (on tape they do, but why would they on memory cards?)

So DVCPRO-HD could theoretically get down to 40 megabits for 24fps. That would give you maybe 11-12 minutes on a 4gb card.

Now, DVCPRO50 is already 50 megabits, about the same data rate, so you should get 10 minutes of footage on that 4gb card.

I don't believe DVCPRO50 supports any sort of progressive-scan repeat-frame mode, I believe (and could be dead wrong) that it's the same type of 60i system as regular DV, so there probably aren't any duplicate frames that could be completely dropped (unless they implemented some sort of 2:3:3:2 pulldown frame-drop trick... did they do this on the SPX800?) If so, you could record 40-megabit DVCPRO50 data as well, getting maybe 12 minutes per card. But I don't know if that's technically feasible. Seems possible, but...

I of course differ to barry but I was of the understanding that the only camera so far to make use of the dvcpro100 format so far was the varicam. This worked by recording the entire 60 frames per second (regardless of frame rate) and then when the frame rate was set for something other then 60 frames it would flag those frames. Hence when it would record "30 frames progressive" every other frame would be flagged so on playback the tape would "know" what frame rate it was supposed to playback on. This however did not change the amount of data recorded to tape it was always 100Mbps (and to be honest Ithought it was megaBYTES per second not bits, I'm probably wrong here to but 100 megaBITS seems extremely low.) I'm sure the new panasonic camera (whenever it comes out) will be capable of doing some other miracle transformation that allows you to get more minutes per hard drive space but I think the stats I listed above are accurate for the varicam.

There have been at least three DVCPRO-HD cameras, there's the VariCam, the new HDX400 (a 1080i camera), and there was another 1080i camera earlier. There may have been more.

DVCPRO-HD is 100 megabits on tape. HDV is 25 megabits, HDCAM is 140 megabits, DVCPRO-HD is 100.

As far as how the VariCam works, it has a true variable-rate-scanning CCD. The CCD runs at whatever rate you set it for, so it will scan at 4 frames per second, or 60 frames per second, whatever you tell it to shoot at. However, the tape must always record 60 frames per second. So, if you're shooting at 30p, the camera will image 30 frames per second, and will present those to the recorder as soon as they're ready. The recorder will record each "active" frame as it needs to, and then will record duplicate frames until the next "active" frame shows up. So in 30p, there will be 60 frames per second recorded on tape, 30 distinct, unique "active" frames, and 30 duplicated frames (which can be discarded when editing).

For 24P, it runs the CCD at 24Hz, giving true 24p capture. Each frame gets written to tape either two or three times, alternatingly, so it does a 2:3 pattern on tape. Those frames can be removed when editing; FCP-HD can extract the "active" frames, ignoring the duplicate frames, leaving a 40mbps pure 24p file on disk.

This system is necessary because the tape drive must, by definition of the format, record 60 frames per second. It is anticipated that the P2 memory-recording system will not have to abide by that restriction, so it could record only the active frames, thus saving substantial space.

This workflow (duplicate frame rates) is only employed in the 720p version of DVCPRO-HD. In the 1080 version, it always records 60 interlaced fields per second (just like DV does) so there are no "active" or "duplicate" frames.