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From Camera to Edit Suite

Dec 1, 2004 12:00 PM, By Steve Mullen

The first in a two-part report explains how to manage HDV camera output for editing on HD systems.

Charts
Audio/Video Sync and Video Quality

Until recently, if you shot HD you generally used either the HDCAM or DVCPRO HD formats. Then you used a post suite that had the appropriate playback deck. HD decks transfer uncompressed video using an HD-SDI connection. Multiple channels of digital audio are sent from the deck to your NLE either via AES/EBU connections or embedded within the HD-SDI signal.

This straightforward procedure is becoming more complicated because our friends at Sony, Panasonic, and JVC have several new HD formats coming your way. The first, HDV, comes in two flavors: 720p29.97 and 1080i29.97. The former has been shipping from JVC for over a year. Sony recently started shipping the latter in the United States. (See “Sony's HDV Debut” in the October issue.) Both use 4:2:0 MPEG-2 encoded at 19Mbps and 25Mbps, respectively. At NAB 2005 Sony likely will introduce 4:2:2 MPEG-2 at 80Mbps recorded on XDCAM blue-laser media. Panasonic has already announced that it too will offer an MPEG-2-based HD format that is recorded to P2 media.

It would be wonderful if all these new HD formats could be edited with the equipment already in place at post suites. If not, then producers will naturally choose shooting formats with an eye toward where it can be edited. This adds a concern to the investment in any of these new formats.

Thankfully, there are ways to eliminate this concern. In this article, I'll show you how to bring 720p30 HDV into an HD editing system. This will be a prototype technique that can be used to handle incoming MPEG-2-based HD formats. While I'll be using Final Cut Pro, the same techniques can be applied to other NLE systems.

For now, here are four things you need to know. First, I'm not going to be dealing with the 24fps versions of HDCAM and DVCPRO HD. Second, HD-SDI (SMPTE 292M) is a technology of sending 4:2:2 uncompressed digital video and, optionally, digital audio, ancillary data, and metadata at either 1.485Gbps or 1.485/1.001Gbps. Specifically, a SMPTE 292M bitstream comprises two interleaved streams, one containing 10-bit luminance (Y) samples, the other 10-bit chrominance (CrCb) samples. Both 1080i and 720p are supported.

Third, camcorder-shot HDCAM source material has a temporal rate of 59.94 fields per second, while DVCPRO HD source material can have a frame rate of 59.94 or 60.0fps. Fourth, HD-SDI can be used to send HD video from your NLE back to your HD VCR.

The input and output of HD-SDI requires a PCI board for your Mac or PC. (Of course, Panasonic's new AJ-HD1200A also supports DVCPRO HD input/output via FireWire.) Multiple channels of digital audio can be embedded within the SMPTE 292M bitstream or passed via AES/EBU connections.

AJA kindly loaned me three of their products for my experiments: the HD10A (MSRP $3,200), HD10C2 (MSRP $1,190), and a Kona HD board (MSRP $3,995). The tiny HD10A accepts YPbPr (or RGB) analog via three BNC jacks. The HD10A digitizes the analog input and then converts it to a bitstream that is available on three BNC HD-SDI output jacks. I used a 75Ω coaxial cable to connect the HD10A to the Kona HD input BNC.

While you would normally connect the Kona HD output directly to your HD deck using an HD-SDI connection, I'm not blessed with one of the beasts. Without an HD deck, I connected the Kona board's single output BNC to the HD-SDI input BNC on the HD10C2, again using a 75Ω cable. A large jack on the tiny HD10C2 box accepts a supplied plug and cable that terminates in three BNC plugs. The HD10C2 converts the HD-SDI bitstream to baseband digital video that is passed through three digital-to-analog converters within the box — and output via three BNC connectors. I connected the three BNC (YPbPr) plugs to my LCD projector so I could use it to view the Kona HD output.

My projector and the AJA HD10A accept 720p59.94, 720p60, 1080i59.94, and 1080i60. A DIP switch on the HD10A allows you to select either 59.94 or 60Hz video input. The Kona HD is slightly more limited, accepting only 720p59.94, 720p60, and 1080i59.94.

When one outputs analog component video from a JVC HD1 or HD10 camcorder (or a CU-VH1US mini-deck), the 720p29.97 HDV is decoded to base-band digital video. This video is passed through three digital-to-analog converters and output from the camcorder. You have the option to select All To 480i, All To 480p (neither of which you want), No Convert, and All To 1080i. If you select No Convert, every frame is sent twice (1/60 second apart) which yields 60fps progressive video. If you set All To 1080i, the 1280×720 pixel video is upconverted to 1920×1080 pixel video. Odd and even video lines are sent alternately as odd and even fields (1/60 second apart) that yields 60 fields per second interlaced video. That's right, in both cases the camcorder outputs 720p60/1080i60 — not, as one would expect, 720p59.94/1080i59.94 video. This means the Kona HD board can accept only one of the camcorder output formats: 720p60.

How can we obtain analog HD video at 720p59.94 and 1080i59.94? Simply send the 720p29.97 MPEG-2 to a JVC HM-DH30000U D-VHS deck via an i.LINK cable. This deck can be set to output analog component video at either 720p59.94 (mode set to No Convert) or 1080i59.94 (720p To 1080i). (Obviously, do not select All To 480i.) Using a D-VHS deck as an intermediate enables one to use 720p59.94 and 1080i59.94 editing sequences.

These experiments mean that if you already have Kona HD, all you need to purchase are these components: a JVC camcorder or a JVC CU-VH1US, plus an AJA HD10A converter. And don't forget high-quality coaxial cables. In my first attempt at getting this system to work, I tried using cheap cables. The 1.485Gbps bitstream struggled, but failed, to get to and from the Kona HD board.

Many post suites will soon need to accept Sony HDV tapes. The Sony HDR-FX1 camcorder outputs 1080i59.94, so the signal can be fed through an HD10A into a Kona HD board and captured at 1080i59.94. Moreover, because the Sony can play back JVC tapes, 720p should be able to be captured at 1080i59.94.

So far, I have not talked about how HDV audio will be digitized. All you need to do is connect a stereo 1/8in. mini-plug cable between the camcorder earphone jack and your computer's analog stereo input. Now duplicate and then edit the Kona HD Capture Templates that you want to use. Set QuickTime Audio Setting to Built-in Audio and the Device to Line In.

If you are working with a G4/G5 and a JVC D-VHS deck, you can use an optical audio link. Plug an optical cable into the D-VHS deck's optical output port. This port outputs 48kHz PCM audio obtained from decoding the MPEG-1 Layer 2 audio transmitted from the camcorder via i.LINK. In this case, set Device to Digital In within the Capture Template. I found this option worked great and eliminated any possibility of hum or noise pickup. If you want to provide a digital connection from a camcorder's audio output jacks, all you need is an analog-to-digital signal converter (Radio Shack 15-1242) that costs a mere $25. No matter how you transmit audio, you also need to set Device Control to Non-Controllable Device within the Capture Template.

For one of my tests, as I recorded video I periodically used a clapboard to provide a way to check audio and video sync with frame accuracy. I then digitized HDV at 720p60, 720p59.94, and 1080i59.94 to an Apple Xserve 3.5TB RAID. I used both the 8- and 10-bit Kona (Blackmagic Design) codecs. A RAID is required because 1080i video requires a data transfer data rate of 124MBps. (The Kona HD digitizes 1080i at 1920×1080.) A very large RAID is required because an hour of 1080i requires 448GB. And this is using uncompressed 8-bit video. These values increase, for 1080i, to 166MBps and a whopping 597GB per hour if you were to digitize using 10-bit video.

Unfortunately, the 10-bit codec sometimes caused Final Cut Pro to crash at the end of a capture. Also, far too often, a capture could not be stopped, requiring my Mac to be rebooted via its power switch. Equally perplexing, but not as fatal, the incoming video was not always displayed during digitization.

Depending on the magnitude, and the MPEG frame in which it was located, dropouts created varying levels of glitches in the digitized video. Sometimes only a row of macro-blocks was disturbed. Other times, audio was momentarily muted. The worst case was that a frame or two would simply disappear. These results indicate that high-quality DV tape must be used, and you need to avoid stressing it during capture. All this reminded me of working with Hi8 metal evaporated tape.

Once I had clips in Final Cut Pro Sequences, I checked for audio and video sync — as well as video quality. You should be aware that when you play back a Sequence, you must set (View > Video Playback) the correct type of output. Thus if you are playing 10-bit 720p59.94 video, the output must be set to match. I also checked for transfer quality. The table on p. 20 shows audio/video sync with a “+” indicating video leading audio.

I have not yet found a solution for the bizarre results of digitizing at 60Hz. It might be the result of slightly unsteady sync from the camcorder's analog output. The unsatisfactory results from digitizing using 1080i would seem worthy of an in-depth investigation if it weren't for the fact that a conversion from 720p30 to 1080i29.97 isn't an optimal transfer path because it involves a double conversion: both temporal and spatial. If one wants to create an HDCAM production, it makes far more sense to use the new Sony HDV camcorder. Using a Sony camcorder makes even more sense if one plans to intercut MPEG-2 HD with HDCAM material.

Thankfully, the 720p59.94 digitization succeeded. However, while motion was smooth, I did note both vertical and horizontal “combing” on fast motion. As I examined timeline footage frame by frame, I noted two characteristics. First, as expected, each frame was repeated. Second, each frame had two displaced images within it. This was not expected. Of course, this was the first time I could examine the analog output from the JVC products. Part Two of my experiments, coming next month, will look further at digitizing HDV.

I didn't expect, nor did I see, any quality differences between the 8-bit and 10-bit Blackmagic codecs. No matter which codec was used, picture quality was outstanding.

These hardware procedures should also work with future MPEG-2-based HD formats. Blue-laser and P2 decks will certainly have HD-SDI output.

My experiments have convinced me that post houses that handle HDCAM and/or DVCPRO HD can also handle MPEG-2-based HD. This means you can feel relatively free to choose any of the new MPEG-2 HD formats and be confident that a post suite that is currently editing HD can establish a way to edit HDV. The only caveats are that optimal results will be obtained only when a progressive/interlaced production is created from progressive/interlaced source material (respectively), and when temporal rates match.

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