This article describes how to get the best video capture frame rate with your Power Macintosh G3 computer.

Optimizing Video Capture Performance

In general, there are a few things you can do to optimize video capture performance.

The Power Macintosh G3 minitower with the Audio/Video card can support up to 320- by 240-pixel video capture at 30 frames per second. This rate is for capturing video only. This rate decreases if both audio and video are captured simultaneously.

Most video capture applications use standard QuickTime Video and Audio settings. How you set these settings can affect the performance of video capture significantly. The PowerMac G3 Read Me included every Power Macintosh G3 computer states:

Video capture is available on Power Macintosh G3 computers with video input and output ports.

• The video capture feature works with Virtual Memory (VM) on, but the quality of captured video improves if VM is turned off. AppleTalk should also be made inactive while capturing to prevent network activity from introducing slight variations in the quality of captured video.
• The monitor connected to the built-in graphics port should be set to Thousands of Colors and the capture window size should not exceed 320 x 240 pixels. The best compression to use with this computer is Component Video.
• If you have difficulty capturing video or the captured video looks very pixelated, try reducing the resolution and/or number of colors on the monitor connected to the built-in graphics port.
• If you have a monitor connected to the built-in graphics port and another monitor connected to a PCI graphics card, then to capture video you must have the video capture window of whichever application you are using completely contained on the monitor connected to the built-in graphics port.

System Configuration :

Extensions Manager Settings :

• Select Mac OS 8.1 or 8.5 base Set
• Duplicate set and save as QuickTime Capture (this will be your Extensions set when you want to capture video).

Load only the following control panels at startup :

• Control Strip
• Memory
• Monitors & Sound
• QuickTime Settings

Load only the following extensions at startup :

• ATI 3D Accelerator
• ATI Graphic Drivers
• ATI Graphics Accelerator
• ATI Video Memory Manager
• QuickTime
• QuickTime PowerPlug

Memory Settings set in the Memory control panel :

• Disk Cache = 256K
• VM Off
• No RAM Disk

AppleTalk Settings :

• AppleTalk turned off in the AppleTalk Control Panel

Monitors & Sounds Settings :

• Color Depth = Thousands
• Resolution = 832 x 624, 75Hz

Sample Capture Settings for Video Capture Application

Not all settings below are available in Apple Video Player.

Video Capture Window location :

Place the video capture window in the lower right corner of the screen. Video capture performance is optimized when the video capture window is outside the rect 0,0,320,240.

Audio Input Settings :

• Sound Off

Video Input Settings :

• Record at 320 x 240 Compression

Component:

Video Depth:

Color Quality: High (75) Frames per second: 29.97 (29.97 fps is the actual NTSC standard)

Mac OS 8.5 Video Capture Enhancements

The video capturing software for both Power Macintosh G3 and PowerBook G3 Series computers has been significantly enhanced for Mac OS 8.5. In addition two compression settings now directly support capturing. These are the Component Video and Photo-JPEG compressors.

Figure 1 Video settings (compression settings shown)

At quality settings of Medium or less, full rate captures (29.97 frames/second for NTSC, 25 frames/second PAL and SECAM) can be achieved for capture sizes of 320 x 240 or less.

Additionally, under Mac OS 8.5, video capturing is now more tolerant of other system activity. Full rate captures can now be achieved when using Component Video or Photo - JPEG at 320 x 240 or less, even with AppleTalk enabled, File Sharing active, Virtual Memory enabled, and sound being captured.

Note : 320 x 240 captures using Component Video result in over 4.5 MB/second of data being written to the hard disk. Apple uses hard drives from a wide variety of hard drive vendors, and some hard drives might not be able to sustain that data rate. This results in dropped frames.