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Old February 18th, 2012, 10:21 AM   #1
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DVD Bit Rates short projects

In the past I've always just picked a default render format from 1080i to DVD video stream and results have varied. For this 38 minute project I would like to get better results and manually set the render bit rates. Typically my projects are in the 35-40 minute range. Audio is AC-3.

I've reviewed Ed's very helpful newsletter on bitrates to help me get started. With Vegas 11 the default bit rates are 9,500,000, 6,000,000, and 192,000. For my current project I'm considering increasing the avg rate to 8,000,000 and increasing the min rate to 4,200,000 . Is the max and min too high?

What would be your bitrate recommendations for similar projects in the 35-40 minute range? Would I be better off just using CBR and setting it to 8,000,000? Using a bit rate calculator I see that I should be able to set CBR even higher than 8,000,000.

In addition, I'm using 2 pass and best rendering, upper field first, interpolate. Any comments along these lines?

Thanks.
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Old February 18th, 2012, 11:23 AM   #2
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Re: DVD Bit Rates short projects

For a short project, I'd probably just use 8,000,000 to 8,500,000 using CBR. If you have enough space and can use a high enough bitrate, there's really no reason for VBR.
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Old February 19th, 2012, 08:42 AM   #3
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Re: DVD Bit Rates short projects

Thanks Ed. I tried a few different CBR rates and even with a rate of 9,500,000 the rendered video file size was only 2.66 GB. I chose this rate based on Vegas showing it as the maximum VBR rate. I hope I don't run into a problem playing it on some set top DVD players, As a general rule do you think it should have a lower maximum rate?
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Old February 20th, 2012, 08:00 AM   #4
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Re: DVD Bit Rates short projects

I'm leery of going to 9,500,000 because some player can't handle that rate - especially when maintained over a longer period of time. I've always felt safer limiting it to 8,500,000 but if it's working fine for your needs, feel free to use it. One would think that players today should be able to handle the max allowed rate.
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Old February 20th, 2012, 09:21 AM   #5
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Re: DVD Bit Rates short projects

+1 Edward's recommendation.
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Old February 20th, 2012, 10:08 AM   #6
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Re: DVD Bit Rates short projects

Also, it depends on the type and quality of the blank DVD media. With any DVD-R media or a low-quality DVD+R disk, it is best to keep the total bitrate (video, audio, menus, etc.) to no higher than 6,500,000. That's because the tracks on DVD-R is less readable than those on most DVD+R media.
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Old February 20th, 2012, 10:27 AM   #7
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Re: DVD Bit Rates short projects

Thanks all. For my final Vegas project I used a bit rate of 9,000,000 and it's plays fine on my set top DVD player.

In DVD Architect when I choose to Make Disk - Burn - Optimize , I noticed I also have a bit rate choice.
Should the bit rate here always be set to the same as the rendered file bit rate?
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Old February 20th, 2012, 10:35 AM   #8
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Re: DVD Bit Rates short projects

When rendering to MPEG in Vegas if the bitrate is right to beging with DVDA should just take the rendered A/V without having to optimize or re-render so I wonder if the bitrate is too high to start with which would give you a file size that a standard DVD can't accept without re-rendering. Keep in mind that typically a DVD isn't 4.7 gigs of useable space but somewhere in the range of 4.34 gigs. Has to do with formatting of the disc.
Since I've been using DVDA (started when it first came out) I have never run a bitrate about 8,000,000 as my max. Before I switched to TY WaterShield discs I used Verbatim printable and only had a very occassional disc that wouldn't play in some set top DVD players. Since I made the switch to TYs, when they first came out, I haven't had one disc that won't play.
Again I keep the max rate at 8 and the minimum at 2,000,000 and adjust the average rate as needed for the length of the product. Edward has a chart in one of his old newsletters that I've been using since he produced it and it still works for me today although I've re-printed it a few times.
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Old February 20th, 2012, 10:36 AM   #9
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Re: DVD Bit Rates short projects

Hi

The maximum combined video and audio rate for DVD is 9.8Mbits/sec. So for 9500 you only have 300 left for audio, if you go above this on the audio you are breaking the specification. Some software will work this out and tell you however Sony Vegas doesn't seem to take the audio into account when setting the video bit-rate.

There should be no problem using a constant bit-rate at the maximum provided the combined video and audio doesn't exceed 9800, however VBR with a high average bit-rate and high minimum allows some leeway and also helps make some use of the video buffer (albeit a small buffer on DVD), which allows the data rate from the buffer to exceed the maximum streaming rate from the physical spinning disc for challenging footage, it also gives a bit more room for read errors for dirt or damage while not reducing picture quality.

Assuming your audio is AC3 at the maximum quality for DVD at 448Mbits/sec, then something like 9200 maximum bit-rate with a 9000 average and minimum 8000 should give the picture quality benefits of the maximum possible constant bit-rate with the extra resilience a lower bit-rate achieves.

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Phil
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