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Old May 8th, 2003, 01:26 AM   #1
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Subtitle bitrates?

How much of the DVD's bitrate do subtitle streams use?

Do I have to count them all together even only one is displayed at a time?
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Old May 8th, 2003, 06:22 AM   #2
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Yes, you have to count EVERYTHING together. The whole package
CANNOT exceed 9.8 mbps. In each package all the video, audo
and subtitle packets will be present. I cannot remember how much
each subtitle track adds (they are basically compressed stills)
but it isn't much. Each dolby audio track (5.1) adds 384 kbps if I am
not mistaken and dts normally stays under the 1 mbps. If you
encode your video at around 5 mbps you should be save to add
a couple of other things
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Old May 9th, 2003, 08:43 AM   #3
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Why....is 9.8 mb/s the max bitrate DVD players can read?
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Old May 10th, 2003, 06:29 PM   #4
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<<<-- Originally posted by Glen Elliott : Why....is 9.8 mb/s the max bitrate DVD players can read? -->>>

Correct, set top DVD players, that's the spec. You can actually exceed that for short segments, but it's because it's buffered ahead. Sustained, max is 9.8 mbps. Subtitles need to be counted, but generally take up very little room if they are not animated.

///d@
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Old May 11th, 2003, 08:16 PM   #5
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So say if I encode at 9.9 mb/s (CBR)...I will definitly run into problems? Will the DVD player be able to read it at all? I'm not planning on trying to encode at anything higher- I'm just curious as to what would happen.
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Old May 11th, 2003, 08:24 PM   #6
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My software warns me the bit rate is too high. I suspect some players would try to play it and probably freeze, others just wouldn't play. Don't know for sure, I never wanted to waste a disc to find out.
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Old May 13th, 2003, 11:28 AM   #7
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Glenn,

Do NOT overencode! It might work on your player but
it is simply not garantueed to work. That is what we have
standard for! The standard of DVD just does not allow the
bitrate to go over 9.8 mbps TOP. That's it, case closed.

Stay within the guidelines and you should be safe. Don't add
more problems to the mix!

Oh, we are talking about mbps (megaBITs per second) not
MB (megabytes) per second! Your authoring software and
mpeg2 encoders know how to handle all of this.
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Old May 14th, 2003, 04:45 AM   #8
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Does anyone really know the _actual_ subtitle bitrate per used subtitle stream?

"Not much" might become "significant" if you have 8 different subtitle streams.
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Old May 14th, 2003, 07:36 AM   #9
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<<<-- Originally posted by Jami Jokinen : Does anyone really know the _actual_ subtitle bitrate per used subtitle stream?

"Not much" might become "significant" if you have 8 different subtitle streams. -->>>

It is not a fixed amount, it's based directly on subtitle image complexity and frequency of change. Simple subtitles that come on, stay on long enough to be read, and go away, even time 8, is still (I'm guessing) well under 0.1 mbps.

I suggest you build some subtitles that match what you'll need in your project (a few minutes worth of text changes) and measure the bitrate that you get, then multiple by 8.

For your first disc out of the gate with 8 subtitles, it would be better to error on the safe side, so don't try to max out your bitrate to the full 9.8 mbps.

///d@
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Old May 14th, 2003, 11:42 AM   #10
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Dennis gives good advise, just try it out and see what you get!
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Old May 15th, 2003, 03:53 AM   #11
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Yes, and if it turns out that the guess of "under 0.1 mbps" is three or four times too low, it still way lower than I thought it would be.

So if I play safe and count e.g. 0.3 mbps for total subtitle streams, it still leaves me generous amount of space for video and audio.

Thank you for your help guys.
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