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Calculating file size of MPEG2 & AC3

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Cutter_Jones
Calculating file size of MPEG2 & AC3
on Oct 19, 2007 at 5:57:04 pm

Hello,

I tried a search for 'calculating file size' and did not see results related.

What is the best way to calculate the file size of encoded MPEG2 and AC3 files of a video, before you actually do any compressions?

I am trying to plan ahead for a client. We have one 45-minute video we produced and will be authoring to a SD DVD. The issue is that they want to create a DVD kit that will contain 12 foreign language versions of this 45-minute video. The audio of each version will have voice over read in the relevant language. And the video will have graphics written in the native text of each language. So each version needs to have it's own video and audio track on the DVDs.

I'm trying to calculate how many DVDs will be needed to contain 13 versions of this 45-min video (1 English, 12 foreign languages).

Thanks for the help.


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epontius
Re: Calculating file size of MPEG2 & AC3
on Oct 21, 2007 at 2:56:40 pm

Do a google search for "dvd bitrate calculator or DVD bit budget.

The trick is that AC3 audio is encoded at a constant data rate depending on the number of channels (2ch ac3 is .192 Mbps). In other words it's the only variable you can't change. Most of these bitbudget calculators, add up the total time of your video to calculate how much space is taken up by the audio, then subtract it from the capacity of your disc, leaving the remainder (with some overhead) available for video. Since the video can be compressed at different bitrates, they then calculate the video bitrate making sure that it will fit in the remaining space on the disc.

Erik


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