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Why dv & dvcpro to p2?
Why it is said everywhere that camera records dv _and_ dcpro25 to p2?
What’s the difference in ntsc with these two?
(In pal dv is 4:2:0, dvcpro 4:1:1) -
13 Replies
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Bitstream-wise, in NTSC, there’s no difference that I know of. As you pointed out, in PAL, DVCPRO retains 4:1:1 color sampling which is a difference.
Also DVCPRO employs locked audio vs. the DV standard of unlocked; however, the DVX100 and the JVC DV500/DV5000 use locked audio anyway, so I would expect that the HVX will employ locked audio whether in DV or DVCPRO mode.
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As these signals are written to tape DVCPRO 25 is 18 micron track pitch; DVCAM is 12 microns and DV is 9 microns. Although the compression schemes are the same I suppose there may be embedded instructions on where the data is placed along the tape physically to give you the footprint of each format. As I understand it, as the helical head writes a frame on the moving tape, the footprint is elongated so instead of square it is sort of diamond shaped, like a slightly pushed over square. As the next one is written the top of the footprint hangs over the toe of the last one. With DV these footprints only slightly overlap but with DVCAM there is more overlap and with DVCPRO this overlap between frames, as it is physically written, is quite robust. This is an advantage for the editing decks as they are able to follow the signals better with the wider track pitches.
This is how I understand it anyway, maybe someone else can sync us up on this issue. -
Pitch widths are 18, 15 & 10
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It makes a difference to me as I’m set up with DVCPRO and would rarely use DV if I want to output to tape. Now if they would only change the transport…
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But if dv and dvcpro25 are identical in p2, what’s stopping you to export dv from p2 to dvcprotape to be as dvcpro25?
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[Rennie] “Although the compression schemes are the same I suppose there may be embedded instructions on where the data is placed along the tape physically to give you the footprint of each format.”
I’m suggesting that there is meta data embedded in these formats that distinguishes the track pitch, audio tracks location, tape speed or footprint length, location of time code etc. when outputing to tape. Sony may have the T/C along the top and Panasonic along the bottom.
[toke lahti] “But if dv and dvcpro25 are identical in p2, what’s stopping you to export dv from p2 to dvcprotape to be as dvcpro25? “
The compession scheme is the same for the actual video picture but there is hidden data there that the decks and cameras use to read and write. Also the physical location of timecode and sync ect may be in different locations on the different brands of formats. Therefor these formats are not identical, just the picture compression part is identical. The P2 format preserves this formula for which ever format we choose so when we output to tape it plays in the deck of the format we chose.
I’m no engineer and I’m really just guessing here but it makes sense to me. -
Rennie,
Well, in your post you said you were just guessing, but that sounds like a d@mn good guess to me.
One thing that I find interesting with P2 technology, is that once Sony embraces it (they’ll have their own proprietary brand of it that will only be compatible with Sony gear, of course) then I believe their DVCAM format will no longer have relevance, as once “tape speed” is done away with, then DVCAM’s advantages go kaput.
Anyone wanna chime in on this or correct me on this one?
jeremiah black
dual 2 gig G5
2.5 gigs of RAM
Decklink Extreme capture card -
[toke lahti] “But if dv and dvcpro25 are identical in p2, what’s stopping you to export dv from p2 to dvcprotape to be as dvcpro25?”
Nothing — provided you’re in NTSC mode. The bitstream is identical, so you could execute a firewire dub from DV to DVCPRO25 tape.
If you’re in PAL, you’ll have a problem, as PAL DV is 4:2:0 and PAL DVCPRO25 is 4:1:1, so you couldn’t do a firewire dub of that.
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I don’t belive that there will be any tape specs in p2’s video file.
Video clip in p2 is in file format, which is totally different than data stream which is recorded to tape.
Storing data about eg. “where to put tc” in the tape or “what is track pitch” would be useless, because the deck knows these things already and can’t change them.
If these kind of ristrictions would exist you couldn’t copy dv to dvcpro and vice versa. -
[toke lahti] “Why it is said everywhere that camera records dv _and_ dcpro25 to p2?
What’s the difference in ntsc with these two?
(In pal dv is 4:2:0, dvcpro 4:1:1) “A SIMPLE EXPLANATION
If there is no embedded meta data as I speculated and there is no difference it would seem to be for streamlined marketing and manufacturing. If the same body casting is used in both pal and ntsc models the selection switch could be the same and the reference markings on t he body (be they decal or raised plastic text) could be the same. A 4 position switch could indent from DV; DVCPRO
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