reducing bitrate for longer DVDs

slambubba wrote on 5/1/2005, 8:54 AM

i'm converting analog Hi8 tapes to DVD for a friend at work. one DVD for the wedding and another for the reception. i'm using AC3 stereo for the audio in vegas. the wedding is 75 minutes and i used an average bitrate of 6,000,000 (default) when rendering to MPEG2. the reception is 135 minutes and i used an average bitrate of 4,200,000. for both, i set the minimum bitrate to 2,000,000.

i played the 135 minute DVD on three players. on one of them, it frequently had a mosaic pattern. on another, it did every once in a while. on my computer DVD, none at all.

i'm using a DVD+RW and i'm wondering if it could be this or the lower bitrate? can lower average bitrates cause problems with some DVD players? the player that had the most problems with the DVD+RW usually doesn't like them.

any feedback is appreciated.

Comments

John_Cline wrote on 5/1/2005, 9:05 AM

I think this is more about the quality of your discs as opposed to the bitrate. What brand of DVD media are you using?

John

slambubba wrote on 5/1/2005, 9:38 AM

fuji 2.4x DVD+RW. i've used them many times, so maybe they're getting scratched, dirty, etc.

B.Verlik wrote on 5/1/2005, 10:17 AM

Players that play +RW are still in a minority. Make sure all your players are capable. Some players have better luck with certain brands of disc than others. There are probably plenty of posts here, telling which +RW work best with most players, but I'm still using -R and can't tell you that information.
I've made DVDs with an average of 3,800,000 bps for approximately 2Hr and 15 Min DVDs and have not had any problems yet. Use 2-Pass VBR, when you lower the bitrate to get a clearer picture.

johnmeyer wrote on 5/1/2005, 10:18 AM

This is almost certainly NOT a bitrate issue, especially given the relatively low bitrates you are using. With may players, the re-writeable discs (DVD+RW and DVD-RW) are just on the "edge" of readability. Thus, if you do have a disc that is a little dirty, or perhaps just starting to wear out (although you are supposed to be able to re-write hundreds of times before this happens), you might start to get readability errors, which would visually show up in exactly the manner you describe.

If you have a cheap DVD-R or DVD+R disc that you can spare, try burning on that and see if you have a problem. I bet it will play just fine.

slambubba wrote on 5/1/2005, 11:21 AM

thanks guys.

will 2-pass VBR double my render time?

Avanti wrote on 5/1/2005, 2:04 PM

yes, but worth it.

johnmeyer wrote on 5/1/2005, 5:08 PM

will 2-pass VBR double my render time?

As already noted, the answer is yes. However, It may or may not produce big benefits. 2-pass is primarily useful only when the bitrate gets really low. I define really low as 4,000,000 bps. Between 4,000,000 and 6,500,000 you will get some benefit, especially if you have long stretches of relatively low-motion video, followed by bursts of really fast motion. (There is nothing magic about these numbers: they are just my estimates).

Finally, if you have a video that has about the same amount of motion in every scene, then you are not going to get much benefit from 2-pass at all. The only way 2-pass can help is if the encoder can use very few bits to encodes low-motion scenes, and then use the bits "saved" in this way to encode at a higher bitrate for the high-motion scenes.

I just managed to put over three hours of golf (all four days of the Masters, on four discs, each 3+ hours long) on single-sided, single-layers discs. This was a project made for 2-pass because there is almost no motion in 90% of the scenes, especially as the golfer stands over the put, or as they show the scoreboard. This provides a huge "cache" of bits that can be used when the golfer tees off or actually walks across the green.