Sunday, October 30, 2005

JVC HD100U frame rates

Last weekend I went up to Hollywood Studio Rentals to demonstrate the CineForm products as part of the DV Camps training seminar (www.dvcamps.com.) I've done this show before when the JY-HD10 was first launched two years ago. This time around the gear was for more suitable for the filmmakers that were in attendance. The Prospect HD work-flow combined with the new Wafian on-set recorder was demonstrated operating with the new JVC GY-HD100U. For this demo we captured the JVC's 60p analog feed (through an AJA HD10A digitizer to output HD-SDI) into the Wafian disk recorder; then, just a moment later we sent the captures data via GigE to the Prospect HD editing system for playback and editing as either a 60p clip or a prefect 2.5X slow-motion at 24p. This seemed a crowd pleaser.

Although CineForm products fully support all the JVC's modes over FireWire, capturing directly from the analog feed has several quality benefits. Bypassing the MPEG compression of HDV is significant one, yet there is also the increased chroma resolution of 4:2:2 vs HDV 4:2:0. Even for users of the HVX200 will get both resolution and chroma image enhancements by bypassing that camera's DVCPRO-HD 720p compression which has a normalized (to 1280x720) sampling resolution of 3:1½:1½. There are also frame rate advantages, particularly for HD100 users. When the JVC camera is in 30p mode the analog output is at 60p, similarly for the 25p mode the analog feed is 50p; so what happens at 24p? I expected a 3:2 pulldown of the 24p into 60p (somewhat like the 24p mode does on tape), however the camera actually puts out a true 48p with a 1:1:1:2 pulldown into 60p. This means for standard shooting/slow-motion rates, that options are 24, 25, 30, 48, 50 and 60 frames per second. With additional selective frame recording, correctly cadenced frame rates of 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 16 and 20 fps are also available. How cool is that? Really, I want feedback on this so we can determine what sort of capture frame rate controls are implemented within Prospect HD and similarly within the Wafian recorder. The JVC HD100 is shaping up to be an excellent indie filmmaker camera.

6 comments:

Isaac said...

Great Blog David!
Keep up the good work!!!

From Kosovo,
Isaac

Jason Rodriguez said...

Hi David.

Very interesting device.

BTW, you may also want to look into the identification and removal of the tagged frames on the Varicam. That would give the opportunity for stuff like speed-ramps, etc.

Also the Varicam can record quite a bit of dynamic range in film record mode (see the article by Michael Bergeron of Panasonic at the HPA 2004 retreat-I think it's bee taken offline, but if you want a copy, I can get it to you), but unfortunetly if you record to the DVCProHD codec in the manner they describe for wide-dynamic range recording, the footage comes out mush. After talking with Michael at NAB 2004, he basically said you need 10-bit recording to take advantage of the full-dynamic range the Film-Rec mode can offer (which of course makes perfect sense).

So again, this may be a feature you want to look into, especially since a recorder like this makes for a great alternative to HDCAM-SR or D-5, but neither of those decks can detect the redudant "tagged" frames on the HD-SDI output of the Varicam (the HD-SDI frames are tagged though).

David said...

We definitely intend to add that support. Message to Panasonic (or anyone with a Varicam) : please send us a test tape with various frame rates recorded.

Jason Rodriguez said...

sorry I don't have a tape readily availble for you, but if I'm not mistaken, the master and repeat frames are tagged in the User Bit of the SMPTE timecode stream.

Jason Rodriguez said...

Here's more info from the Panasonic site:

How do I convert variable frame rate footage shot with the AJ-HDC27 VariCam back to 24fps footage ?

Panasonic offers a hardware based Frame Rate Conversion to provide this function and is working with key NLE manufacturers to provide full support for variable frame rate digitization and conversion functions. As previously described, the VariCam adds additional frames via the process of pulldown at the camera section output in order to make a constant frame rate of 60 frames per second at 720p resolution recorded on tape - a HDTV standard 720p/60 signal format. This pulldown sequence necessarily varies as the camera frame rate varies, so in order to identify which of the frames recorded to tape have new information, and which frames have repeated information, the VariCam writes into the timecode user bits recorded on tape a mark for all "Active" or "new information" frames. Frames that are simply "Repeat" frames -- that is, frames duplicated by pulldown process in order to create a standard 720p/60 HDTV recording -- do not carry the mark data.

David said...

Thanks, I think we have this information, it is an issue of testing only. We have a DVCPRO-HD deck but only footage shot at 720p60.