The recordable DVD capacity FAQ

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owlsroost
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Joined: Dec 5 2000

The recordable DVD capacity FAQ
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Q: The disc says the capacity is 4.7 GBytes, but my authoring software says it's 4.38 GBytes - how come ?

A: Disc manufacturers assume: 1 GByte = 1000 x 1000 x 1000 bytes, but computer software normally assumes: 1 GByte = 1024 x 1024 x 1024 bytes. So 4.7 (disc manufacturers) GBytes = 4.38 (computer software) GBytes

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Q: What duration can I fit on a recordable DVD authored as a DVD-Video disc?

A: Anything up to 6 hours or more - it just depends on the quality you need.

As a rough rule of thumb for various frame sizes (assuming a good MPEG encoder):

Using 720 x 576/480 ('D1'), up to 2 hours at good -> very good quality, up to 3 hours for average quality.

Using 352 x 576/480 ('half D1'), up to 4 hours at good -> average quality (but the pictures will be softer overall due to the reduced horizontal resolution).

Using 352 x 288/240 ('SIF'), up to 6 hours at better than Video CD quality.

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Q: How do I work out what bitrate settings to use when encoding ?

A: To roughly fill a disc to capacity, use the formula:

Total Video + Audio bitrate (kbps) = 600,000 divided by the duration in minutes.

e.g. for 120 minutes, total bitrate = 600,000 / 120 = 5000 kbps.

Subtract the audio bitrate from the total above to get the target video bitrate

e.g. for 384 kbps MPEG audio, video bitrate = 5000 - 384 = 4616 kbps

(Note: if using standard LPCM audio, the audio bitrate is fixed at 1536 kbps)

The video bitrate value above is the average (not peak) value for variable bitrate (VBR) encoding, and the bitrate value for constant bitrate (CBR) encoding. Also the formula is bit pessimistic, and most encoders also 'play safe' so don't be surprised if the files come out smaller than expected.

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Q: Should I use constant bitrate (CBR) or variable bitrate (VBR) encoding ?

A: In theory, VBR encoding should provide the best balance of quality versus disc space, but the results will vary with different encoders and different source material so it's best to try it and see.

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Tony

[This message has been edited by owlsroost (edited 26 July 2003).]