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Firewire vs P2 recording- no im not starting another debate
I was trying to remember the differences in recording to firewire vs. P2. If I recall, the difference was that the firewire output flagged frames in a 60p stream and the p2 recording only recorded the actual framerate used.
I know thats slightly off, what was it again?
And are there any other differenced between the recorded streams?
Wouldnt it make sense for the firestore folks to use a p2 interface to the hardrive… instead of firewire? There are benefits going that rout but like i said I cant remember them!
Emery
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3 Replies
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The data that gets recorded (whether via firewire or onto a P2 card) is identical, in all of the 1080 modes or for 720/60p, or for DVCPRO-50 or DVCPRO-25 or DV. All the same flags, etc., are all included.
The only circumstance where anything is different at all is in 720p mode, when you’re recording at less than the full 60fps rate. For those circumstances, P2 will drop duplicate frames and only store the active frames, whereas the firewire streaming signal will include all 60 frames (appropriately flagged for removal).
The stream is kept consistent at 100mbps so it will work compatibly with other products (such as the AJ-HD1200A firewire-enabled DVCPRO-HD deck).
If the Firestore people want to take advantage of space efficiency, they could probably intercept the signal, detect duplicate-frame flags, and drop those frames, and only record the active frames for 720p mode. The flags are there in the stream, so there would likely not be much benefit to them trying to interface through a P2 slot.
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Get the most from your DVX camera. The DVX Book and DVX DVD are now available at https://www.dvxuser.com/articles/dvxbook/ and at Amazon (https://tinyurl.com/54u4a) -
Barry (or Jan), a quick question for you…
Why is the HVX capable (at least in P2) of recording the necessary discreet frames at lower frame rates in 720p, yet in the 1080p modes records inside the 1080 60i stream? Was there some technical reason for this?
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Yes, because the original DVCPRO-HD codec wasn’t designed for 1080/24p. The 720p codec was designed from the beginning to support variable frame rates. The 1080 version is designed only as an interlaced codec.
When recording 24p in 1080, the camera has to employ the same 2:3:3:2 or 2:3 pulldown as used on a DVX or SDX. This involves flagging the start of an interlaced sequence (the “A” frame of a five-frame group). With 720p, each and every frame gets flagged “active” or not. In 1080/24p, there’s only one flag, at the beginning of each group.
It’s recorded that way and then piped out the firewire that way. Doing it this way makes the camera compatible with tape decks and capture applications that are expecting to see a full 100-megabit DVCPRO-HD signal.
Now, as to why P2 doesn’t know how to remove pulldown from the 1080 signal in the same way that it knows how to remove “inactive” frames from a 720 signal… that’s a good question. It’s probably because no editing system knows what to do with a 1080/p file, because up until the HVX there hasn’t been such a thing as a DVCPRO-HD 1080/progressive signal…
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Get the most from your DVX camera. The DVX Book and DVX DVD are now available at https://www.dvxuser.com/articles/dvxbook/ and at Amazon (https://tinyurl.com/54u4a)
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