What is "peak bitrate" ????

Derek Miner

Screenwriter
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Feb 22, 1999
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The highest possible rate of data playing on a DVD is about 10 megabits per second. This includes all items associated with the video track, such as soundtracks and subtitles. In a simplified sense, a Dolby Digital 2.0 track takes about .18 of a megabit and a 5.1 track takes about .44 of a megabit. The sound rates are constant, but the video rates fluctuate. The number of megabits left after subtracting the rates for the audio and subtitles (which I understand to be negligible as far as "bit budget" goes) you get the highest possible video rate. But the video on the DVD only very occasionally reaches that limit. Actually, it seems to me the length of the video content on the DVD is a bigger factor than how many audio tracks there are. The numbers above indicate you can put five 2.0 tracks on something and you still could get a pretty good maximum bit rate for video. But if you have to encode 4 hours of video rather than 2, the levels won't approach that peak very often.
 

Brian W.

Screenwriter
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Jul 29, 1999
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Brian
I seem to recall reading (years ago) that a DVD will hold about 20 minutes per single-layer side at peak bitrate. Does that sound correct?
 

MarkHastings

Senior HTF Member
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Jan 27, 2003
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Does the 10 Mb peak include all of the track combined? I thought it was just the video and any one of the audio tracks (i.e. the max only accounts for the currently playing A/V stream)...

In most cases, the video portion is never allowed to go over 8Mb - That gives the disc plenty of room to add a high quality audio track and the subtitles.
 

MarkHastings

Senior HTF Member
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Jan 27, 2003
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Hmmm - If you take 10 mb/sec...

That's 10 mb / 8 MB = 1.25 MB per sec

1.25 MB x 60 seconds = 75 MB per minute

if a single layer DVD holds approx. 4,500 MB (i.e. 4.5 GB)

4,500 MB / 75 MB = 60 minutes.


I think my math is correct....
 

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