Barry Green
Forum Replies Created
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On the Varicam, variable frame rates are indeed recorded as 60p on tape. They’re imaged at the appropriate frame rate, and then duplicate frames are created to pad the sequence up to 60p, because that’s what the tape mechanism needs in order to be able to record.
On the P2 card, such gyrations are not necessary at all. It directly records only the frames it needs, so a 30p sequence takes up half as much space as a 60p sequence. Only the 30 frames per second are stored; there are no duplicates.
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It’s my understanding that Focus already offers an MXF file converter program that should do exactly what you want.
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[Eric Jurgenson] “If, presuming 2.5″ or 3.5” HDD’s can handle the 12.5 MB/s data rate of DVCPRO HD, will the HVX200 have the ability to spit live video out the FireWire to an external field drive?
Yes, it can already do that. Any manufacturer who develops a Firestore or QuickCapture-style device, and can handle the data rate, could make a drive to do exactly what you’re asking. Already (if the camera were here now) you could plug it into an NLE and capture the data stream straight to hard disk.Is anyone making a portable drive at this point that will function as a DVCPRO HD field recorder and directly mount on an NLE (without copying)?
Yes, Focus is developing a FireStore to do exactly that. And Serious Magic is working on HD Rack for DVCPRO-HD. And other manufacturers may offer products as well.How about a device that would allow easy use and swapping of commodity SATA drives, while containing the power and 1394 interface in a field hardened enclosure? This would be hard to beat in terms of cost and speed.
That’s what I’m hoping for. Basically a DVCPRO-HD version of the FireStore FS-3.On another note, does the HD RAID requirement for current P2 cards on the HVX200 mean that it is impossible to record uninterrupted HD video for more than sixteen minutes? Then if you want to continue recording, you have to buy another set of P2 cards or wait while your files are transferred to a hard drive in the field? Does this field transfer device exist at this point?”
P2 can record indefinitely as long as you keep hot-swapping cards. There is a field device (the “P2 Store”) which automatically copies the contents of a card onto its internal hard disk and erases the card, ready for hot-swapping back into the camera. If you had enough storage available, you could record for hours and hours uninterrupted by continually hot-swapping cards.—————–
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[Peter DeCrescenzo] “Wouldn’t it be easier & faster for the cam’s electronics to simply _copy_ the redundant frames (for example, the 6 frame difference between 24 fps and 30 fps) instead of _compressing_ the redundant frames? Those 6 frames are identical, right?
No, those frames are never identical to any other frames. The pulldown frames are created from taking a field from the prior frame and a field from the next frame. So, in 2:3:3:2 pulldown (the most compression-efficient mode), you have four full frames, followed by a fifth that is made from half of one and half of the other. Sort of like AA/BB/BC/CC/DD. Since the recording format is interlaced, the frames get split into fields for recording (same as in HDCAM 24PsF). The “fifth frame” is made from one “field” of one frame and one “field” of the other. Not a duplicate of anything else.
If a cam’s in 24 fps mode, I’d expect it to allocate relatively little of its processing muscle to record 6 redundant frames onto tape, and instead spend more of its time and horsepower to better-compress each of frames 1-24 (in 24 fps mode) than it normally would to compress each of frames 1-30 (in 30 fps mode).
In a GOP-style system, that is what happens. In DV, or Digital Betacam, or M-JPG, or MPEG-IMX, that’s not how it works. Every frame is compressed separately, regardless of anything happening in any other frame. So every frame gets the exact same compression applied to it, whether it’s a duplicate or not.That’s why the data rate is so much lower in DVCPRO-HD’s 720/24p mode when recording to P2; duplicate frames are simply dropped, they’re not compressed at all. So instead of taking up 100 megabits of space, it only occupies 40. Each frame is compressed the same, but there are fewer frames, so it takes up less space.
But are you saying that’s not how it works? Or does it depend on the cam/model?”
It depends on the recording format. DV or any of its variants, and any other frame-based codec (such as, again, Digital Betacam or MJPG etc) all encode frame-by-frame. So does MPEG-IMX, which is an MPEG codec but is intra-frame only. Long-form GOP compression, such as MPEG-2 HDV, can take advantage of frame duplication to get more efficient compression for the frames it does compress.—————–
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May currently be vaporware, but there was a news story that Toshiba is pouring some bucks into one of the manufacturers. Might help solidify that vapor!
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Your question about 24 or 30, and repeating frames etc., depends on the type of compression scheme used.
DV, for example, is always always always 29.97fps (or 25fps for PAL) and it doesn’t matter whether you are recording 24 within 29.97 — it always has to compress all 29.97fps.
Same with DVCPRO-HD in 1080i.
In 720p, DVCPRO-HD encodes each frame individually, regardless of frame rate — so slower frame rates take up less space.
All those compression schemes (including Digital Betacam, DVCPRO50, MPEG-IMX, etc) are all frame-discrete, and what happens in one frame has no effect on another frame.
With long-GOP MPEG-2, (such as BetaSX or HDV), what happens in one frame has a direct relationship with what happens in other frames. Those compression schemes don’t encode each frame discretely, instead they encode the changes between frames. That can lead to much more efficient compression, as well as to disastrous dropouts (but dropouts are rare).
So, JVC records 720/30p in HDV at 19 megabits. But for 24p, it would seem that they would get more efficient compression — fewer frames in the same bitrate. However, apparently (and this is not 100% confirmed, but I think it’s 90% confirmed) JVC’s 24p is actually recorded as a 60p data stream, with lots of duplicate frames (obviously 36 of the 60 frames are just duplicates). MPEG-2 can be quite efficient on duplicate frames, so it’s possible that HDV will get complete efficiency on many/most of those duplicate frames. But with a GOP of 6, and the frame repeat pattern running at 5 (2:3 frame duplication), it’s unclear whether HDV is getting the most efficient use of its GOP. But from all reports it’s still pretty efficient — presumably it will be the least-compressed of all the HDV variants.
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Any data storage technology is a candidate for backing up. DVCPRO-HD tape is probably the least desirable way to go, because you lose all metadata. Hard disks, Blu-ray or HD-DVD disks, even DVD-R disks (a regular DVD-R backs up a 4gb card easily, a dual-layer backs up an 8gb card).
But as Jesse said, a data tape backup system might be the most cost-efficient way to go. Perhaps a DLT or comparable system.
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[Marion Laney] “1) Is there or will there be a device that I can simply insert the card into which can playout DVCPRO100 via HDSDI or Firewire into a 1200a deck with matching TC??”
You could certainly dub from the camera (or computer) to the AJ-HD1200A deck. As to whether it will dub timecode… I’m not 100% sure, but I’d say there’s a 95% chance that it will… presumably it will, but until we actually try it, there can’t be any guarantees.
[Marion Laney] “can I get a true DVCPRO100 signal out a HDSDI output on the camera itself?
None of these low-cost HD cameras offer HD-SDI. The only way to get HD-SDI would be to use an analog-to-HD-SDI converter, but I don’t know if you would be able to preserve timecode.
Someday someone (like Miranda) may offer a firewire DVCPRO-HD-to-HDSDI converter. I believe they’ve just created one for HDV, so it certainly seems reasonable to expect one for the HVX as well. But I don’t think such a device exists yet.
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[Shane Chadder] “If the Avid codec works with Premiere, can you purchase the codec separately?”
You don’t need to purchase it, you can download it free.
https://www.avid.com/onlineSupport/supportcontent.asp?contentID=7952Just be aware that it only works in Quicktime, not in AVI’s. I don’t know if it will work with Premiere, but it works in Vegas so presumably Premiere Pro will support it as well.
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If you’re editing in a 29.97 timeline, then using regular 2-3 pulldown will give slightly smoother results. 2-3-3-2 (“advanced”) pulldown can still be used, it just isn’t quite as smooth as 2-3 pulldown (when viewed in a 29.97 timeline).
If you’re using Sony Vegas, converting from 24PA to 24PN is instantaneous — just open a project in 29.97, and make sure “allow pulldown removal” is checked. When you put a 2-3-3-2/24PA file on the timeline, it will automatically, on-the-fly convert from 24PA to 24PN and give you the smoother pulldown.
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