More DV NLE Gotchas
Feb 1, 2003 12:00 PM, By Bob Turner
Don’t forget connectivity issues, storage gaffes, and other potential problems that can slow down your work.
 The hard disk you choose to handle media is a major issue. An Ultra DMA/ATA-100 drive with 7200 RPM or more, like this Seagate Barracuda, offers excellent performance. |
As I discussed in last month's column, buying a DV format editing system involves considering many options before you decide on a system. There are many “gotchas” that can come between you and your DV NLE. To avoid these, I have listed some of the issues you should consider when purchasing a DV-format NLE.
Last month, I covered software and hardware choices, and how to choose a VCR to work with your system. This column will focus on connectivity issues, storage options, and miscellaneous other gotchas that can make life with your DV NLE difficult.
Connectivity Ports
Connectivity is a concern that you should ponder carefully when buying a DV-format NLE. While FireWire (aka IEEE 1394 or i.LINK) is the most common connection, there are alternatives and reasons for considering an alternative method. For example, you will not be able to do frame-accurate insert editing through FireWire. Audio issues, including the ability to input alternate audio-only sources, audio synchronization delays, and the ability to mix audio tracks prior to entering them into the NLE system are also problems associated with inputting media through FireWire. Depending upon system configuration and source, there may be issues of timecode accuracy, and source transport controls may not function properly.
Apple and Panasonic have already announced that they are working on a next-generation FireWire 800 (IEEE 1394b) connection that will handle 800Mbps video streams and feature other improvements. While we will have to wait for the specifics, 24p/variable frame rate and connections to less compressed formats will be the primary benefits. Most software manufacturers will eventually develop drivers for the new, faster-throughput connection.
Another FireWire gotcha is using an incompatible IEEE 1394 interface card. Generally, an Open Host Controller Interface (OHCI) should be used to connect devices. This is an industry standard endorsed by Microsoft, Apple, Hewlett Packard, Intel, Sun Microsystems, National Semiconductor, and Texas Instruments, among others. The standard is designed to ensure that software drivers and applications are compatible with OHCI-compliant hardware.
Alternative connectivity options include RS-422 transport control with SDTI or SDI inputs/outputs, and USB or USB 2.0 connectivity. The RS-422 transport control is the industry-standard VCR control interface and has been for decades. It is almost always frame accurate and bulletproof. The SDI connection is the granddaddy standard for digital video — especially for connecting uncompressed video between devices.
The newer SDTI standard, an industry compromise between the compressed digital video interface proposals put forth by Sony (QSDI) and Panasonic (CSDI), offers metadata container standards and a way of ingesting media at four times normal speed with VCRs offering this capability.
The USB port is being used for DV import by a number of Windows-based computers. The USB 2.0 standard is competing with FireWire for dominance as the “digital pipe” of choice for high-bandwidth throughput needs. The technologies and capabilities are comparable.
Storage Options
The hard disk you select for your media is also a major concern since this is another potential bottleneck. The disk must be fast enough to handle the performance you require, and most software manufacturers recommend keeping your media on a separate hard disk. Frequently they will qualify specific hard disks and drive controllers.
As a general rule when working with a DV-based nonlinear editing system, this hard disk can be a second ATA drive. An Ultra DMA/ATA-100 (7200 RPM or greater) with the proper hard disk controller card will offer excellent performance.
An external IEEE 1394 or USB 2.0 drive is another popular alternative storage solution. This does not require a space for the hard disk within the computer nor does it add heat to the platform's interior. These external drives are actually ATA hard disks with a connection bridge and external housing. Those with internal power supplies appear to last longer and work better.
Also, look for an Oxford 911 bridge chip specification or the new Oxford 922 bridge chip. This technology was designed to work with FireWire nonlinear editing platforms. If using this method of storage, use properly shielded high-quality cables and connectors.
Associated with FireWire and USB connections is the problem of ganging multiple devices and having the system not be able to handle the configuration. Sometimes changes in OS system settings and BIOS need to be addressed for a configuration to work. The most common problem is attaching a camera and an external drive and then using both simultaneously. Some editors with qualified cameras and external drives have no problem, and others give up after trying to make their configurations work. You should only use devices specified by the system manufacturer. If problems still occur, try changing the position of the devices in the FireWire chain or try shorter cable lengths.
A Small Computer System Interface (SCSI) storage solution costs approximately twice as much as ATA storage, but benefits include far greater performance and generally a much better warranty. SCSI hard disks are frequently the disks of choice for RAID storage systems, but manufacturers such as Medéa have begun to offer storage systems utilizing the less expensive ATA drives in a RAID configuration and with a SCSI connection interface. Other manufacturers that offer lower-cost RAID drives include Rorke Data, Huge Systems, MicroNet, and Promicro Systems.
An excellent resource for additional information on storage configurations and other configuration issues is a white paper written by ProMax president Charles McConathy, “Configuration of Non-Linear Digital Video Editing Systems.” It is available at www.promax.com/PDF/NLESystems.pdf.
Another storage option is one that allows you to record direct to hard disk in the field, and then use that disk as your media storage with your editing system. Fast Forward Video, Focus Enhancements, Granite Digital, Laird Telemedia, SmartDisk, and Sony are among the manufacturers that offer such solutions.
The last storage solution I want to mention is a Storage Area Network (SAN). These networks are especially common at post facilities and educational institutions, although even a personal project studio might have shared storage with a graphics computer or a digital audio workstation. These systems offer shared storage and software for media asset management, including management of shared metadata. With the advent of Gigabit Ethernet as a low-cost alternative to Fibre Channel networks, SAN solutions are becoming more popular.
 External drives are a popular storage solution. This external USB drive from Western Digital comes in 40GB, 80GB, and 120GB sizes. |
However, having a SAN does not guarantee that multiple users will be able to access the same footage at the same time without ill effects. SAN manufacturers include Rorke Data, Studio Network Solutions, JMR Electronics, DataDirect Networks, Hewlett Packard, Dell, Network Appliances, and Huge Systems.
Another storage concern is archiving your media. Removable hard disk solutions and optical media are two of the more popular alternatives today. The continual plummeting of the cost of hard disks makes removing them and storing them practical — at least short-term through lengthy client processes, or even long-term by charging the clients for the hard disks the way you might charge for videotape. Optical storage is becoming another nearline solution, especially with optical disk servers from Asaca/Shibasoku or PowerFile. A simpler, lower-cost solution might be a DVD burner that can serve the dual purposes of archiving and creating media for distribution.
Other Gotchas
Monitoring is a major gotcha with many DV-based editing systems. There are color space differences between IEEE 1394 I/O and NTSC I/O, but how do you monitor them? Unless you have a realtime video output that can go to external waveform monitor and vector-scope, you must render any questionable video segments and then play the rendered segment out to WFM/VS monitoring for analysis.
Does your audio synchronize with the video when playing the timeline or ingesting? Is the monitoring an accurate representation of the audio/video stream? This is frequently a function of configuration and setup parameters, but the process of confirming these parameters can be confusing.
Locked versus unlocked DV audio is another potential gotcha. Locked audio is the preferred method, but due to the cost of a locked audio clock, the format standard provides for the less expensive “unlocked audio” alternative. The total amount of sync slippage allowed in unlocked audio is +/- 1/3 frame, but this can result in pops at edit points and other difficulties. (Note: This variation does not cause audio to drift out of sync because the variation is not cumulative in one direction; the video and audio clocks are still linked.)
To complicate audio matters further, DV records at three different sampling rates: 32KHz, 44.1KHz, and 48KHz. (44.1KHz is always unlocked, but the other two sampling rates can be locked or unlocked.) This can result in incompatibilities in output formats, incompatibility between audio clips in the time-line, incompatibilities between work-group workstations, and other woes. The fix is care in production and proper deck and NLE setup in the post process.
Another concern is generational loss. Many will say, “But this is digital!” It is true that digital clones are identical, but every video process requires an uncompress/recompress process. When the selected codec uncompresses the video, it has to guess what the missing bits in the uncompressed video looked like. If you go through this cycle too often, the errors are cumulative and degradation can become noticeable.
Choosing software with the best codec algorithm can make a difference. Fortunately, codecs are constantly improving, but you should be aware of the “state of the art” at the time you buy.
Some other gotchas are not post-oriented. Timecode breaks/restarts on DV tapes are one example. Cameramen sometimes black their camera original tapes (recording silence, black, and timecode) before going out in the field to shoot. Many camcorders will see and reset to that timecode. If batch input is necessary, sometimes the only solution is to do a digital dub of the camera originals, laying in new continuous timecode.
The safest ways to prevent DV gotchas are to educate yourself about potential pitfalls, make wise investments, and create proper workflows adapted to these new technologies.
Bob Turner has edited video on nearly every piece of equipment ever made. He can be reached at bobturner@attbi.com.
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