Consistent Dropped Frames Only During Capture

Symptom #1: Dropped Frames Even Though You Can Play Back the Same Content from the Scratch Disk

"I get dropped frames warnings very shortly into every single capture, although I can usually play back the same type of video content that is already on the scratch disk."

"I get a dropped frames warning every time I try to capture or play back anything at all."

Background

If you're getting dropped frames consistently, even though you're sure your Mac and other hardware meets the requirements of the format you're working with, you may have an inadequate storage solution.

Four factors of your storage solution are critical to capture and playback: bus speed, drive speed, overhead (extra bandwidth needed for the file system and other activities) and free (unfragmented) space. Other factors, such as the formatting of your drive, partitioning scheme, and RAID level can also affect the performance of your system. Since capture is a more intensive process than playback, you may find that you drop frames during capture, but not during playback.

Higher-data-rate formats, such as uncompressed standard and high definition video, will generally require RAIDs that are striped together using software or a proprietary hardware card. If a RAID isn't configured correctly, you can expect trouble.

There are some features that, although ideal for convenience, may impact performance. For example, Xserve RAID uses a feature called RAID Now, allowing a RAID volume to become available as it is being built. Another fantastic feature is the ability to restore the contents of a RAID 5 disk while maintaining availability of the RAID set. In none of these circumstances do you want to capture high-bit-rate video while these processes are in progress.

Other factors, such as background processes on your computer can also affect storage performance. When you first install Mac OS X 10.4, or when you add a new storage volume, Spotlight performs a thorough indexing of your mounted volumes. This activity can take many hours depending on the size of the volume. While the indexing takes place, you can expect some degradation in your hard disk performance.

Solution

Make sure that your storage system's bus speed, drive speed, and overhead are adequate for the technical requirements of the type of video you want to edit. Lesson 7 covers the specific requirements of the various video formats.

Symptom #2: Consistent Dropped Frames After Capturing and Deleting Lots of Footage

"I've been capturing lots of footage and deleting it. Lately I get a dropped frames warning every time I try to capture anything at all."

Background

Even when formatted correctly, disk performance declines when data on the hard drive becomes fragmented. The problem occurs because data is located on different parts of the drive rather than contiguous blocks.

If your storage system is set up and formatted correctly and is not fragmented, but you are still experiencing consistent dropped frames, your storage system may not be in good working order.

Solution

• Make sure your drives are fast enough.

• Not all drives perform equally. For example, you can significantly increase the performance of your Xserve RAID by using 400 GB drive modules, rather than 250 GB drive modules.

• Drives that provide acceptable performance internally may not perform at their optimal level in an inexpensive FireWire enclosure. Consider both the drive manufacturer specifications as well as the control and interface specifications when purchasing external drive storage.

• Make sure you have ample disk drive space and that drives are not too fragmented.

The Mac OS X startup volume should have a minimum of 250 MB, and preferably 375 MB, of free disk space available. You may need more free disk space to install a system update. Keep as much disk space available as possible.

Equally important is the free space available on your storage disks.

If you have a dedicated hard drive (or at least a dedicated scratch disk partition), erase your hard disk prior to your capture session. If you are working with existing media and have room on another partition, you can use Disk Utility to create an image of your media partition, then erase and restore your media partition using your backup. (You can learn more about using restore images from Disk Utility Help.)

You can also use Disk Utility to verify and repair data and permissions on your disk, identify the S.M.A.R.T. (operational) status of your hard disk, as well as identify the format and partition structure of your disk.

To defragment your hard disk, you can use a third-party disk utility (choose Apple menu > Mac OS X Software). Remember to back up your data before you defragment your disk.