Consistent Dropped Frames During Capture or Playback

Symptom #1: Dropped Frames When a Camera or Deck Is Connected to a FireWire Drive on the Same Bus

"I'm capturing DV from my camera onto my FireWire drive using my PowerBook, and I'm constantly dropping frames."

Background

This problem involves using a FireWire daisy chain, which is tempting but not recommended. If you have a camera or deck connected to a FireWire drive on the same FireWire bus, you're setting yourself up for dropped frames or device-related communication issues.

Although FireWire 400 has a theoretical speed of 400 megabits, or 50 MB/s, not all devices can communicate over FireWire that quickly. DV decks and cameras, in particular, work at much slower data rates, usually at a standard 100 megabits, or 12.5 MB/s. Thus, your FireWire drive, which normally can deliver a data rate of 16 MB/s (because it is a single physical drive), might be able to deliver only 5 or 6 MB/s when placed behind a DV deck on the FireWire bus.

Dropped frames due to a congested FireWire bus are rarely a consistent problem, but they become more likely if other factors are present. Say you are working with a Mac that has 512 MB of RAM, a relatively fragmented drive, and a deck on the same FireWire bus. Any one of these factors alone might not cause an immediate dropped frames warning, but the three together are quite likely to cause problems.

Solution

If you're working with video formats other than DV, don't use a FireWire drive for capture or playback of your project. If you're working with DV, keep the camcorder and FireWire drive connected to different FireWire buses. Although your Mac may have up to three FireWire ports, there is only one FireWire bus.

Note

If you have a newer PowerBook or desktop PowerMac with both a FireWire 400 port and a FireWire 800 port, you may still get dropped frames due to FireWire bottlenecks, because the two different standards share the same FireWire bus on the motherboard.

The way to add an additional FireWire bus to your system depends on the type of system you have:

• If you have a PowerBook, you can use a PCMCIA FireWire Cardbus card. Having the scratch disk FireWire drive connected to a completely different bus from the DV deck eliminates the possibility of data-stream bottlenecks. (iBooks don't have a PCMCIA Cardbus slot.)

• If you have a PowerMac, consider adding a PCI FireWire expansion card. Although you can locate the deck or camera on one port and other FireWire devices on another, both FireWire ports share the same bus, so you can still get bottlenecks. A FireWire expansion card provides a completely separate FireWire bus.

Symptom #2: Dropped Frames with a New FireWire Drive

"I'm getting dropped frames warnings with a new drive I recently purchased."

Background

The key to trouble-free FireWire drive use is to remember that a FireWire drive is just a normal ATA drive attached to a FireWire cable. You have to treat the FireWire drive just like any other drive you might employ in FCP, with regard to standards, throughput, maintenance, and upkeep.

Solution

Make sure that the FireWire drive is fast and large enough to support the video format you are working with. For instance, many editors working with FireWire DV may want to use FireWire drives for storage. The DV format isn't particularly demanding, but you must set the minimum drive specifications at 7,200 RPM.

Also, make sure the bridgethe device that converts data on the drive into a data stream that can travel to the Macintosh and backis of recent vintage, such as the Oxford 911 (FireWire 400) and 922 (FireWire 800) chipsets. Some of the earliest FireWire bridge chipsets offered irregular throughput that didn't utilize the full potential of the FireWire 400 50 MB/s data rate.

If you are working with a more demanding format, such as uncompressed 8-bit or HD footage, you may get slower throughput. Theoretically, FireWire 800 has enough throughput to handle both of these formats, but if the drive isn't fast enough to handle the data rate, it doesn't matter how fast data can travel through the cable. The drive is usually the slowest link in any media storage chain. Consult Lessons 8 and 9 for information on data rates and storage solutions.