Probably a stupid question about Re-sizing video

[bluevine]

I want to see if I can "shrink" a video in size. For example, when playing a VCD on my TV, I'd like the image to take up only a portion of the screen rather than the full screen. The movie image would be centered on the screen and surrounded on all sides by a black border. My theory is that the resolution might appear better because it would be streched over less space. Perhaps I'm dreaming but I assume this can be done somehow. It may be useful where the source is a poor analog VHS tape.

I'm using Pinnacle Studio 7 to Capture. I then use VirtualDub to framserve into a MPEG using TMPGEnc. Then I'm using VCDEasy to burn.
Normally, when I setup TMPGEnc for the MPEG creation I set it to 4:3 (NTSC).

At what point in my capture/convert/burn process could I "downsize" this image without effecting its proportions.
Many thanks

[El Torro]

I think you want the 16:9 Format(sounds kewl these days ) ya, well you know how to resize in TMPGenc, try resising to 16:9 in stead of 4:3... That will give you what you want(i think, i'm not 100% sure since i never do/did that)

[banjazzer]

My theory is that the resolution might appear better because it would be streched over less space.

I think the theory is wrong. You will be using part of the bitrate to encode the black border, and less pixels will be allocated to the picture.

[bluevine]

I hadn't thought about the black part taking up the bit rate but you're probably right. Part of my theory was that a video looks good when played on WMP which takes up only a portion of a 17 inch PC monitor during playback. However when viewed on my 35 inch TV it doesn't look as good.

Wouldn't changing the size from 4:3 to 16:9 simply destort the image to some degree and only add the black bars at the top and the bottom?

I'd love to come up with a way to do what I'm describing and see the results for myself.

[banjazzer]

If you are viewing on a widescreen TV then unlocking the TMPG template and choosing 16:9 may suit you better. I don't think this will alter the aspect ratio of your encode. However, I don't know for sure because I always leave it as 4:3 even when viewing on a widescreen TV.

I think maybe your 35 inch TV is perhaps revealing the limitation of VCD. Most widescreen TVs allow you to alter the size of the image, so I don't see a lot of advantage in encoding smaller and then emlarging. At the end of the day, you still have a resolution of 352x240(288). It is best that all these pixels are used for the movie.

[MITSUI_1]

Geez... you guys are off base in several ways.

Point, the first:

Yes, you can use TMPGenc "center, custom size" mode to arrive at the black borders you want.


Point, the second:

Encoding the "black" space takes almost NO SPACE in the MPEG stream, AS LONG AS your border starts on a macroblock border. (multiples of 16). If you understand how MPEG works, you'll know why this is the case. If not, you'll just have to believe me.

Therefore, if you resize a VCD to center, custom size = 320x208 but tell TMPGenc to encode standard VCD resolution of 352x240, you will have a black border around the screen. Due to the "overscan" areas, you'll not see this border on most TVs on the sides.


Point, the third:

You will have better quality doing it this way, because bits that would normally be used to encode the data on the "edges" will now be allocated elsewhere. You will have increased the bits per macroblock per second measure, which is a "good thing" (TM). Don't believe me? Take a clip, encode ith 352x240 "regular" mode at cbr 1150, then the same clip at 352x240 but with center, custom size = 320x208, also at cbr 1150. Now load those two clips into the "Bitrate Viewer" software. Notice that the one with borders has lower average quantization. The higher the quantization, the more information the encoder had to throw away in order to meet your specified bitrate. Ergo, put the borders on and you have more quality.

'course, if you actually want to resize it to a super small size with super large borders (i.e., a "4:3 fullscreen" movie with 6 inchies of borders all around), then you'll need to find a guy named Shizzzzon!

(little joke there for the VCD help old skool dudes).

[Thorn]

As you asked how to downsize without changing proportions, I assume you want to send a command to the DVD player/TV to only scan to a certain size. I'm pretty sure 4:3 and 16:9 are the only valid formats, and I doubt anyone put a lot of thought to a display format that didn't use the entire horizontal or vertical dimension (whichever is the limiting factor). There might be a way... but that probably nothing that will play on other people's equipment.

If SVCD is an option, it would be a much better solution. You could have 352x240 pixels of image and still have borders all around. Furthermore, the added bitrate of SVCD over VCD will do wonders for your video quality. The VCD format has troubles with noisy sources sometimes because, since the bitrate is fixed, something has to go when the noise is taking up some of the bandwidth (and that something is the overall quality of the image).

BTW if you put black borders on a vcd, your image will be even more blurry due to having very small dimensions to the actual image. Not recommended. In fact I'd say with a good SVCD encode might be best to leave it fullscreen -- doing some tests is the only way to see what you like best.

[banjazzer]

Geez... you guys are off base in several ways.

Maybe, but I'm not too sure you've arrived at base, either. 8) I know encoding *black space* takes up few bits. However, that is not the main point. If you start with a resolution of 352x240 and use more of the pixels to encode a border, you have less left for the picture. So, you may get higher quality encoding for the picture, but a picture spread over fewer pixels. VCD resolution is already low, so using more of a border makes little sense to me.

Secondly, if you want to use the *center, custom size* setting, then the dimensions you suggest would alter the aspect ratio. It should be 320x218, but still a bad idea IMO.

[bluevine]

I appear to have stirred up an intellectual hornet's nest.
Anyway, I'll give these solutions a try and see the results.
BTW - where in TMPGEnc do you configure the "center - custom size"?

Thanks

[MITSUI_1]

Hi banjazer...

I agree with you in principle -- VCD already has less resolution then we'd like. But with very minimal black borders, most of what you lose is in the overscan area. I.e., it doesn't even show up on most TVs because its off the screen. The way I see it, there's no use using encoding bits for space you cannot see.

As for the aspect ratio, you're right of course. Its not a perfect reduction. Problem is that if you use 320x318 the black borders do not align on a macroblock border and that makes those areas waste a lot of bits, causing the rest of the screen to look like shiznit.

So, what I susually do (but left out of my post in favor of simplicity) is to cut .75 % off of the top and bottom of the PRE-resized image, and then resize to 320x208. This works, as the difference between 318 and 308 is about 1.5 %. (Its also so small a difference you really can't tell the aspect ratio is slightly off even if you don't trim the original).


Best regards,

Mits

[banjazzer]

I can see the point about the overscan area, although I was not aware of a macroblock problem. I have used various resolutions using the *center, custom size* setting, primarily to correct a faulty aspect ratio in the original avi. I never noticed any degradation of quality. Do you have any reference where I can read up about this? Maybe I was just lucky with the numbers I chose?

[MITSUI_1]

banj,

Its really only when you're dealing with a bitrate on "the edge" -- i.e., when you're close to losing quality.

Try the approach I gave above:

Take a clip, encode it twice: once as center, custom size 320x208 and the other at center, custom size at 320x218 -- using the same bitrate and everything else each time.

Then run the results through the "Bitrate Viewer" software and note the average Q for each clip. The higher average has lower quality because the higher "Q" means more information is getting thrown away by the encoder in each frame.

You'll notice a difference visually if you work on the "edge" of where a VCD or SVCD starts to look bad for bitrate starvation.

I'll try to find more information, but that practical test is the best I can do at this time.

[banjazzer]

I will try this. 8) I know mod16 is important with DivX, but i never figured it was a factor with mpeg.

[bluevine]

Mitsui/Banjazzer - I tried adding those borders in Virtual Dub (while frameserving into TMPG). The resultant MPEG1 file indeed had the borders I specified but most parts of the movie which exhibited any motion were very jerky. I encoded the same movie clip without borders and there was no jerky motion. This was just a test using 256x192 as the size of the video with black borders filling out the rest of the 320x240 space. I did notice that encoding the small version took siginifcantly less time than the full-sized version. I'll play around more with this but is the jerkiness a consequence of shrinking the image?
Thanks

[banjazzer]

I wouldn't think so. Are you sure you chose the right template?

[Morloc]

Hey Bluevine,

After reading all of these very technical replies to your original question, I think I have the easiest solution to your problem.

Move farther back from the TV.

Morloc

[bluevine]

Morloc - yeah, maybe if I move far enough back, I'll have an execuse to buy those binoculors I've always wanted.

Banjazzer - I'm using the same template in TMPG to produce the ones both without and without the borders. I did try varying this with that "custom size" option in TMPG but got no better results.