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Choosing bit rates for video and audio
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Choosing bit rates for video and audio
The video bit rate affects both the video quality and the amount of video you can fit on a
disc. High bit-rate video produces a higher-quality image and requires more disc space than
lower bit-rate video.
There are several factors to consider when choosing a bit rate:
• Disc size: Larger disc capacities let you fit more video onto the disc or use higher bit
rates.
• T ype of video: If the video has fast action sequences, or scenes with random motion
such as ripples on water, a low bit rate may result in poor-quality video during those
scenes.
• Source video quality: MPEG compression works best with a high-quality source. If the
original video is low quality — if it has video noise, scratches, and so on — you should
either clean it up in a video editing application or choose a high bit rate to prevent the
quality from getting worse.
• Slideshow and ROM data requirements: Slideshow source files and ROM data leave
less space available for video (see “Effect of ROM data and slideshows on the bit rate
calculation” on page 70 ).
The maximum bit rate allowed by the DVD-Video format is 9.8 Mbps, which must be
divided among the video, audio, and subtitle streams. Although DVD players play only one
audio stream and one subtitle stream at a time, they read all streams off the disc
simultaneously, so you must take the bit rates for all streams into account when calculating
the bit rate.
The following can help you to select the best bit rate for a given video duration:
• “CBR or VBR?” on page 68
• “Bit rate calculation” on page 68
DVDit_Pro_HD.book Page 67 Monday, September 25, 2006 2:32 PM