Encoding to Mpeg2, bitrate converstion Constant or Variable?

[AcuraTL]

I have a 55 minute video clip that I edited in Adobe Premiere 6.5 and I am using Ulead DVD Workshop 1.3 to author it. I am gonig to encode it to Mpeg2 at 8000 kbps. Is it better to use constant or variable bitrate to encode?

[BJ_M]

vbr - well most of the time ..

[AcuraTL]

So is there any advantage in using Constant Bit Rate then? I know the file size would be bigger. Which will yield better quality?

[mats.hogberg]

In theory, VBR would be better, as bits can be used where they are needed, and not uniformely spread over all frames regardless of if there's any difference between them. Better at the same file size.
So, 8000 kbps CBR is less "quality effective" than 8000 kbps average bitrate VBR, provided you have a decent span to max and min bitrates. At 8000 kbps there's not much room left to max (9800 kbps) so I don't think you'll see much difference tho.
The advantage of CBR is that the encoding takes less time.

/Mats

[housepig]

Mats -

assuming for the sake of argument that filesize was not an issue.

also assuming that you have an encoder that can do 9,800 bit rate (maximum bitrate allowable on dvd spec).

Would a VBR 9800 be better than a CBR 9800?

I would think that CBR would be better, as you're throwing the maximum bitrate at it all the time.

And with TMPGenc, where the maximum bit rate you can set is 8,000, if you encode VBR with TMPGenc, will it spike above 8K, or does the VBR only steal bits from low-detail or low-motion scenes to keep the file size down?

[DVWannaB]

I have a 55 minute video clip that I edited in Adobe Premiere 6.5 and I am using Ulead DVD Workshop 1.3 to author it. I am gonig to encode it to Mpeg2 at 8000 kbps. Is it better to use constant or variable bitrate to encode?

Acura,

I believe in the case where you have a 1.5 or 2 hour footage, the VBR is best used to maximize the bitrate, where is some some scenes you may have lots of movement and in some none or very little at all. But in this case, 55 minutes, I would go full CBR at high bit rate (8000 sounds fine). The reason is you have a shorter clip and you can use a very high bit rate and still fit the whole thing on a disk (I am assuming this is the only piece of footage on you DVD disk).

Case in point 1: 55 minute video @ VBR at lets say 2000 low, 9000 high and 8000 average, is not going to look any better or worse than 8000 constant.

case in point 2: 1 hour 45 minute movie @ 2 pass VBR 2000 low, 9000 high, 5000 average, is going to be better than CBR @ 5000. Here you give your encoder a chance to work the full spectrum of the bit rate range and nice allocate bits where it needed most.

Hope that makes sense.

[mats.hogberg]

Would a VBR 9800 be better than a CBR 9800?

Mathematically, no. As you can't go above 9800, VBR with average 9800 == CBR 9800

And with TMPGenc, where the maximum bit rate you can set is 8,000, if you encode VBR with TMPGenc, will it spike above 8K

No idea. If yes, then CBR with 8000 ave, 9800 max and 2000 (or something) min, will look (possibly not noticeably) better than 8000 CBR. But to some extent (pretty much, I assume), it depends on the video - how much motion is going on.

/Mats

[AcuraTL]

I have a 55 minute video clip that I edited in Adobe Premiere 6.5 and I am using Ulead DVD Workshop 1.3 to author it. I am gonig to encode it to Mpeg2 at 8000 kbps. Is it better to use constant or variable bitrate to encode?

Acura,

I believe in the case where you have a 1.5 or 2 hour footage, the VBR is best used to maximize the bitrate, where is some some scenes you may have lots of movement and in some none or very little at all. But in this case, 55 minutes, I would go full CBR at high bit rate (8000 sounds fine). The reason is you have a shorter clip and you can use a very high bit rate and still fit the whole thing on a disk (I am assuming this is the only piece of footage on you DVD disk).

Case in point 1: 55 minute video @ VBR at lets say 2000 low, 9000 high and 8000 average, is not going to look any better or worse than 8000 constant.

case in point 2: 1 hour 45 minute movie @ 2 pass VBR 2000 low, 9000 high, 5000 average, is going to be better than CBR @ 5000. Here you give your encoder a chance to work the full spectrum of the bit rate range and nice allocate bits where it needed most.

Hope that makes sense.

Thanks. That's what I thought. Since I only have 55 minutes of footage, I want to make the quality as high, or the file as big as possible to take advantage of the DVD disc.

[AcuraTL]

In theory, VBR would be better, as bits can be used where they are needed, and not uniformely spread over all frames regardless of if there's any difference between them. Better at the same file size.
So, 8000 kbps CBR is less "quality effective" than 8000 kbps average bitrate VBR, provided you have a decent span to max and min bitrates. At 8000 kbps there's not much room left to max (9800 kbps) so I don't think you'll see much difference tho.
The advantage of CBR is that the encoding takes less time.

/Mats

I tried to do VBR at 8000kps with a max of 9800kps and min 2700kps. When I tried to author it in Ulead Workshop, it tries to re-encode it because it is over their specs, think the file came out to be 9600kps.