Questions about resolutions and bitrate before encoding

[mojo2185]

Attempting to make a XVCD.
I'm trying to match the aspect ratio of my source movie, but I'm having some difficulty. The original movie was 592x320 in PAL at 25fps. I converted the movie and audio to 23.976 NTSC (I need NTSC), but didn't change any resolutions, so right now, the vid stream is still 592x320 (is this ok for NTSC?). In my TMPGEnc project, the current "size" is 352x240, this is the default for the VCD NTSC Film template (should this "size" be changed to 592x320?). I've tried various combinations of "aspect ratios" (such as 4:3 NTSC, 16:9 NTSC) for my stream and likewise for the source, but I can't seem to match my original movie. Can someone explain to me an easy way to figure this out? I've checked out a guide (somewhere on this site) but I'm still confused. Also, someone told me that lowering the resolution could possibly make the picture quality of the encode better. Is this true? Oh yeah, and the film is letterboxed I think (if someone needs clarifying, i can try to post a screenshot).

Last question. I'm trying to fit my movie which is 2hr 18min 28sec on one VCD with as little quality loss as possible. Is VBR the way to go? I've tried the bitrate calculator, and I'm assuming the bitrate it gives me is the "average bitrate" in VBR mode? Even if VBR takes longer to encode, isn't the quality better?

I've had a ton of questions lately because I've finally wandered into the DivX -> VCD area. So sorry for all of my topics/questions that I've put up in the last few days.

Any help is much appreciated!
Thanks

[DJRumpy]

Try this: https://www.videohelp.com/forum/viewtopic.php?t=174200&highlight=

You should have converted your resolution to NTSC as well.

[mojo2185]

Well DJRumpy, thats the guide that left me a little confused. But according to, well, everyone... that's the guide to check out. I will definately give it a second look. I noticed that the guide gives info on SVCDs, CVDs, and DVDs, but not VCDs.
Do I just have to do this equation?
PAL to NTSC: Multiply the vertical by .8334 (i.e 576 * .8334 = 480)

Thanks to anyone who could clarify, perhaps someone could help me with the calculations/conversions necessary for my first time trying? My resolution (according to Gspot) is 592 x 320 (1.850 : 1).

[bugster]

Attempting to make a XVCD.

Last question. I'm trying to fit my movie which is 2hr 18min 28sec on one VCD with as little quality loss as possible. Is VBR the way to go? I've tried the bitrate calculator, and I'm assuming the bitrate it gives me is the "average bitrate" in VBR mode? Even if VBR takes longer to encode, isn't the quality better?

Any help is much appreciated!
Thanks

According to https://www.videohelp.com/calc.htm, this will require a bitrate (average if VBR) of 557kbit/s (using 80 min CD). IMHO, this isn't worth the effort, unless you happen to be encoding a slideshow or presentation of somekind. Use 2 CD's, its worth it.

[mojo2185]

Well, i forgot to update the post, but I've done some editing to the movie. I've cut 5 minutes out of the credits, so that should help. Also, I'm planning on using a lower bitrate for the audio. Doing this, I've achieved an average bitrate of 732. Does lowering the audio bitrate lower the quality of the audio, or how does that work?

Question about Virtual Dub/Cutting and keyframes was deleted, found answer elsewhere

[macleod]

you might want to give dvd2svcd a shot. its at www.dvd2svcd.org (freeware). Basically, all you will need to do is set up your overall template and let it do its thing. Had a home movie that I converted to avi way back when that was a weird resolution (not standard). Put it into DVD2SVCD to make a VCD (and later a CVD), changed some settings and let it go. Worked great.

Probably not the answer you were wanting, but I have suggested this to other people that were having issues and they converted to using dvd2svcd for everything.

[mojo2185]

I've used DVD2SVCD before and it's produced great results as well. Unfortunately in this case, with all of the editing/cutting, framerate conversions, etc... I don't think that would be the best to use at this time for this project.

Definately keep recommending that software though, it really is pretty good.

Thanks for taking a look.

[DJRumpy]

Don't feel bad. Aspect ratio's can get pretty complicated, and even more so when converting between PAL and NTSC. The same rules apply for VCD as for SVCD, CVD, and DVD.

288 * .8334 = 240 (ntsc) so your still using the same rules.

The only odd thing about VCD is the horizontal value, which for MPEG is 352, and not 320. If you do the math for 352x240 video ( 352 / 240 = 1.466 ). It's an odd aspect ratio. I'm guessing the 352 value correlates somehow to the D1 resolution 704 used by DVD. A proper 4:3 aspect ratio for VCD would be 640/2=320, not 352. I have no idea why they do the things they do

An easy way to convert to VCD, is to simply divide your vertical by 2 to get the proper NTSC VCD vertical. For example, if your 4:3 SVCD had a vertical image area of 272, then divide that by two, to get the vertical image area value for VCD.

mojo2185, the guide is a work in progress. If any part of it is confusing, please let me know, and I'll see if it can be expanded, tweaked, or otherwise slapped around to hopefully make it easier to understand. Just PM me or post any comments, good or bad. Every bit helps.

[mojo2185]

592 x 320 is my current PAL resolution... so, lets give this a whirl.
First I'll convert PAL -> NTSC
320 *.8334 = 266.688
so now I got a NTSC vertical... i think...

divide that by 2 to get my new VCD NTSC value...
266.688/2 = 133.344

For horizontal... carry the 1, then...

perfect... errr... maybe not

DJRumpy, your guide really is good, I can see you know your stuff. I'm just new to this aspect ratios and resolutions thing, so its me.

For some reason the numbers just don't add up, could my DivX file just have been encoded at a funny resolution?
Can someone write out the equation with my resolution 592 x 320 (remember needs to be changed from PAL->NTSC) please, so I can see how this works (very visual learner).

Thanks for all your help!

[bugster]

Hmmm, DJRumpy, havn't read your guide, but you said:

The only odd thing about VCD is the horizontal value, which for MPEG is 352, and not 320. If you do the math for 352x240 video ( 352 / 240 = 1.466 ). It's an odd aspect ratio. I'm guessing the 352 value correlates somehow to the D1 resolution 704 used by DVD. A proper 4:3 aspect ratio for VCD would be 640/2=320, not 352. I have no idea why they do the things they do

Correct me if I am wrong, but VCD is aimed at TV display, on which the 'pixels' are not square, so using the horizontal res and vertical res to calculate aspect ratio is invalid. Divx is aimed at PC display, on which pixels are square, so using horizontal res and vertical res to calculate vertical resolution is valid. Is that not right??

[DJRumpy]

592 x 320 is my current PAL resolution... so, lets give this a whirl.
First I'll convert PAL -> NTSC
320 *.8334 = 266.688
so now I got a NTSC vertical... i think...

You've got it exactly. Your video's NTSC equivelent vertical image height. That number, is closest to the 272 value used for 2.35:1 video, meaning your video is probably 2.35:1. You were also right about questioning your AVI's resolution is right at all (this one looks like it is). Remember it's cut and encoded by human hands, and they often make 'adjustements' that aren't right, meaning you could end up with an AVI that has been resized or chopped completely wrong.

592 x 320

Multiply your PAL vertical of 320 by .8334 and you get the NTSC equivelent of 266 vertical (rounded), making the NTSC equivelent of your video 592x266. If you then divide 592 by 266 to get the aspect ratio, you get:
592 / 266 = 2.22 which is pretty close to 2.35.

bugster, I did some digging around, as the thread has aroused my own curiousity. It turns out the 352x240 resolution was defined by the MPEG-1 committee, when they decided to use what's called SIF, for (Standard Interchange format), which split the horizontal and vertical resolutions in half, and then rounded off to the nearest multiple of 16 (for macroblock reason which I know your aware of), which best matched MPEG-1's encoding scheme. The committee also opted for frame-based operation as opposed to fields, which yielded a 352x240x30 fps second standard. This is where the MPEG Aspect Ratio comes in (excert from the link I found...)

- This would tell the hardware decoder exactly how much to stretch the image to display properly on a 4:3 display. The early MPEG-1 hardware decoders that shipped in the 1996 and 1997 did the same thing, in essence shrinking the 352x240 image down to 320x240 for display on a computer screen (note that the vertical is still the same for both displays). However, hardware players never really took off, leaving most computer-based playback to software players, most notably Microsoft's Media Player, which didn't shrink the video, producing an image that looked 10% too wide. Instead, Media Player displayed all 352x240 pixels, expanding the video by about 10%, and adding about 10-20 pounds (TV makes you look fat).

Why didn't Media Player shrink the video? Originally, it was because the underpowered computers of the day had a hard enough time simply decoding the video, much less scaling it down to 320x240. Remember, this was before all computers had graphics cards that could independently scale the video without involving the CPU.

So Media Player merely decoded and displayed the video in its native resolution. The image was distorted by about 10%, but at least it played.

Interestingly, even today, though computers and their high-powered graphics subsystems are more than capable of decoding and scaling MPEG-1 files to the proper resolution, Media Player, now up to version 7.0 (old article. Version 9 does use the aspect ratio in the header), still ignores the aspect ratio instructions in the file header and displays the file at its native resolution, as does RealNetwork's RealPlayer 8.0. In fact, the only player that implements the aspect ratio instructions was Apple's QuickTime Player 5.0.

I'm guessing the hardware in your dvd player still compensates, resizing the image appropriately for a television display aspect ratio, or possibly, the encoder itself compensates. We know this works for PAL video as well, patching the IFO to tell the player your video is 720x480 instead of 720x576. It displays a correct aspect ratio on an NTSC television. Apparently some encoders have a 'square pixel' setting, while othes make the conversion in pixel size automatically. I'd be curious to know what the case is. Regardless, the pixel heights match the output from a DVD when the image heigth of various aspect ratio's are brought into a graphical program and measure.

[mojo2185]

Multiply your PAL vertical of 320 by .8334 and you get the NTSC equivelent of 266 vertical (rounded), making the NTSC equivelent of your video 592x266. If you then divide 592 by 266 to get the aspect ratio, you get:
592 / 266 = 2.22 which is pretty close to 2.35.

Awesome thanks!!!!!

592x266

So, would I enter these new values in TMPGEnc at encoding time, or should I have done this at an earlier time (if so, with what program)? The framerates are already converted.

Thanks a ton!!!

[DJRumpy]

In TMPGenc, the values you enter for your output size depend on the format. If your going to use SVCD, then you would resize your video according to the 4:3 rule:

480 * 1.333 = 640
640 / 2.35 (your movies aspect ratio) = 272
You would resize your movie to 480x272, and select the 'Center - Keep Aspect Ratio' option. TMPGenc will automatically letterbox it for you.

[mojo2185]

When should I have changed the AVI's resolution (from PAL->NTSC)? Should I have done that in Virtual Dub? I haven't started to encode yet so I can always go back.

At encoding time... it will end up being an XVCD rather than a SVCD, how will this change those settings?
Thanks again!

[DJRumpy]

You can resize and add letterboxing in VirtualDub if you want, or you can do the same in TMPGEnc. It's more of a personal preference. Remember the 'Center - Keep Aspect Ratio' setting in TMGEnc will letterbox your video and the additional letterboxing will create a compliant output of 480x480, so you won't have an xCD. Those same settings will work with an input that is already 480x480 ( if you resized in VirtualDub previously for example).