Bitrate for DVD conversion of DivX

[DRP]

I've got a downloaded DivX video of a concert I would like to put on DVD. I would copy the info for the AVI in here but I can't figure out how to export the information from GSpot. Anyway, it's DivX 5.xx, 90mins long and the file is 815MB with a resolution of 640x368.

I want to convert it to DVD including the original AVI file plus some other stuff like the cover scans on the disc as well. The end result of that bitrate calc will be a 704x576 size MPEG-2 with an inside framing of 656x416 to allow for TV overscan with a video bitrate of 1600 < 5155 < 9576 and audio bitrate at 224.

How does that look for what I'm doing? Is an average bitrate of 5155 for this sort of source good enough for the 656x416 resolution?

[jimmalenko]

As the roughest of rough guides, I would say that roughly 3-4x of whatever your DivX bitrate is is generally sufficient, so I think your settings will be well and truly adequate.

[guns1inger]

you are encoding 704 x 576, not 656 x 416. You have to allow for the borders as they are part of the encoded frame. If you want to maximise the use of disk space on your blanks, you could push the average bitrate up to around 6400 - 6500 at that audio bitrate. Will it make a difference - hard to say without knowing the quality of the source, however is there is a lot of movement, every bit counts. (Figures courtesy of the Videohelp online bitrate calculator -> https://www.videohelp.com/calc.htm -> bookmark it, use it.)

[DRP]

you are encoding 704 x 576, not 656 x 416.

Well yes, but I tend to think that TMPGEnc in a 2-pass VBR encode is going to be intelligent enough to allocate a very small number of bits to a completely unchanging black frame around the picture leaving the vast majority to describe the actual 656x416 visible image.

If that assumption is true (and I don't know of any way to actually know whether this is the case or not) then I don't think it is wrong to say that the bits are going to be most evenly spread over the 656x416 frame size rather than the 704x576 one.

I kind of imagine a child's sandbox where the sand has been swept from all around the edges back into the centre again leaving just a small scattering of sand still at the edges. I don't know if that's accurate of course but I suspect only Pegasus know how true it is.

[guns1inger]

It could still be 100-200 MBs over a disk. Not an issue here, but could be if space was tight.

[junkmalle]

Bitrate is probably OK but your aspect ratio doesn't sound right.

[DRP]

Bitrate is probably OK but your aspect ratio doesn't sound right.

It is. At least as close as it can be whilst still being divisible by 16 pixels.

[guns1inger]

If you are encoding for DVD, the 16 pixels doesn't matter.

[DRP]

If you are encoding for DVD, the 16 pixels doesn't matter.

Really?? I thought MPEG-2 was encoded in block sizes of 16x16 or 8x8 or something like that. At least that's what all my SVCD creation guides tell me. What's different about MPEG-2 for DVD than MPEG-2 for SVCD?

Please explain why it doesn't matter.

[junkmalle]

Bitrate is probably OK but your aspect ratio doesn't sound right.

It is. At least as close as it can be whilst still being divisible by 16 pixels.

Sorry, it was late at night. I see you're working with PAL not NTSC so your inner frame size is about right.

Regarding 16X16 blocks, yes MPEG2 does use 16x16 macroblocks. They are then further broken down into 8x8 sub blocks. The full frame size for a DVD compatible MPG file is of course set by the DVD spec. But your inner image can be any size you like.

You might get slightly better results if you inner image's dimensions are multiples of 16 and the image is aligned on 16 pixel boundaries. That way there will be no blocks around the edges of the inner image that are part image and part black background. I suspect the difference will be minimal though.

[DRP]

Yeah thanks, that's what I thought. If this was just so I could watch the video once on a rewritable disc I may not worry about the 16x16 pixel thing at all, but in this instance I'm making the encode to be the highest possible quality disregarding everything else because it's going to be kept and be burnt to non-rewritable disc.

[monzie]

Why not encode at 16:9 and use 672 X 560? (that sfullscreen 16:9 if you have a 16:9 TV less OverScan.)

As for avi (divx/xvid) to DVD conversions I've done a lot of research into this and my conclusion is 2.7 to 4 X the video bitrate of the xvid is plenty, BUT, use around 2200 as a MINIMUM (pref 2500 and above) and I've never come across a typical avi (divx/xvid) that has EVER required more than around 4000kbs for 2 pass...if going single pass CBR go around 4500 to 6000kbs or whatever a bitrate calc gives you using a CUSTOM size.

So 5155kbs will be more than required for 2 pass encoding of your source avi. Go with 4000 if you like and give yourself some breathing space...imo

[DRP]

Why not encode at 16:9 and use 672 X 560? (that sfullscreen 16:9 if you have a 16:9 TV less OverScan.)

You know... that's a bloody good question and one I wish I'd thought of!! I guess I just figured I couldn't use 16:9 because I don't have a 16:9 TV but that's not right is it? I play plenty of retail DVDs mastered at 16:9 ratio and they play perfectly alright on my 4:3 TV so it must work. I guess what happens is that the TV automatically creates the extra bit of black bar top and bottom to get it out to 4:3. Mastering at 16:9 would mean encoding even less black bar and therefore even more efficient use of the bits available for the actual picture. Now if I could just find a little utility to work out the required overscan inner frame sizing required for me instead of having to get all mathematical, it would be easy to do.

As for avi (divx/xvid) to DVD conversions I've done a lot of research into this and my conclusion is 2.7 to 4 X the video bitrate of the xvid is plenty, BUT, use around 2200 as a MINIMUM (pref 2500 and above) and I've never come across a typical avi (divx/xvid) that has EVER required more than around 4000kbs for 2 pass...if going single pass CBR go around 4500 to 6000kbs or whatever a bitrate calc gives you using a CUSTOM size.

Thanks for that suggestion. I was wondering same and decided independently for myself that 4000 was about the sweet spot. More than that appears to make no difference apart from filling up space on the DVD a bit more. Also interested in what you say about the minimum. I had been using 1600 as minimum because that's what I use for SVCD, but it stands to reason I could increase that to the SVCD maximum instead.

I used 1600 for SVCD because that is generally regarded as being the cut point where VCD/SVCD quality meet. So for SVCD I use 1600/2500 min/max, and for DVD use 2500/~9500 min/max

[Abond]

The utility - FitCD

Mastering at 16:9 would mean encoding even less black bar and therefore even more efficient use of the bits available for the actual picture.

Here you are not completely correct (or maybe I didn't understand it correctly). Small black borders - you need more bits to encode the picture, big black borders - you need less bits. So from my point of view 4:3 leterboxed would have more efficient bit distribution than 16:9 anamorphic.

[midnightsun]

Abond is right.

Given the same total size, you get more bits/pixel using more letterboxing (I mean pixels found in the actual picture, it's obvious that the total amount of pixels is the same in both cases)

On the other hand, if you view the 4:3 DVD on a 16:9 TV you'll get black bars on each side (unless you use some trick-like zoom in or something)

[monzie]

Read this thread for more finding OPTIMAL BITRATES for avi's:

https://www.videohelp.com/forum/viewtopic.php?t=255103

And yes FULLSCREEN 4:3 or 16:9 (exact) requires a higher bitrate due to the increased (active) pixel count than anything encoded with borders...but I've taken that into account which is why I suggest a min of 2500 (as opposed to 1800 to 2200 for widescreen with borders)....and yes using the OPV method I've seen OPTIMALS as low as 1800kbs with NO loss in VISIBLE quality (on widescreen 16:9 avis to mpeg) so dont believe a word about 'Bitrate Calculators' as thats only a 'for this space you this bitrate' estimation calc..an idiot can do that in his head (or on paper).

[junkmalle]

Why is everyone obsessed with bitrate? If you don't need a file of a certain size use a Constant Quality mode. Pick a quality level that you're happy with and let the file come out to whatever size it does. And it only takes one pass.

[monzie]

Why is everyone obsessed with bitrate?

Thats the EXACT question I asked myself about a year ago.....the answer is.....'because they know no better'...which is why I found the answer (and how to achieve the optimal bitrate)!