Technical Q&As


QTPC 01 - Audio Samples in QuickTime 2.0 Movies (1-May-95)


Q I need to know the exact frequency to use for audio samples in QuickTime 2.0 movies. I believe that I can either use a 22,050 Hz rate, which is the rate used in the AV Macs and the Power Macs, or I can use 22,254 Hz, which is the rate that the Apple Sound Chip uses. What is the correct sample rate for use in a QuickTime 2.0/Sound Manager 3.0 environment?

A There are actually two answers to your question:

1. In a cross- platform environment, where you would play QuickTime Movies both on the Macintosh and in Windows, use 11.025Hz or 22.050Hz. To play movies using QuickTime for Windows 2.0, you have to flatten them first, and put the resource fork at the end of the data fork. The 11.025Hz and 22.050Hz rates are the most efficient rates you can use, as they are the native Windows sound-card frequencies, and QTW resamples other rates to this rate, resulting in some performance loss (frame skipping and so on). On the Macintosh, Sound Manager 3.0 is better at resampling other rates for platform that have the Apple Sound Chip. We strongly recommend that you use the 11.025Hz and 22.050Hz values.

2. In a Macintosh-only environment, where you would play QuickTime movies only on the Macintosh platform, select a rate that requires the Sound Manager to do as little work as possible. Use 22,254Hz or 11,127Hz for those Macs that have the Apple Sound Chip, and use 22,050Hz for AV Macs, PowerPCs and PB500s.

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