480x576 SVCD to a 480x360 XVID how?

[JeppeK]

I read the guide on converting SVCD to DIVX/XVID with VirtualDub and read that i should resize it to 480x360 and so i did and the result came out beautiful, but what i dont get is how the SVCD that is 480x576 can be converted to a 480x360 XVID and still stay the same size (not loosing anything of the picture)?
Have i done right choosing to resize to 480x360?

This question has probably been asked a thousand times but i didnt find anything when i searced the forum (maybe im a bad searcher?) but i would really appreciate an answer.

Thanks

/Jeppe

(Sorry for my bad english)

[Nelson37]

If you put a slide in a projector and show it on the wall, it has been resized up, but the elements of the picture stay the same. Now, if you were to look at the picture on the wall through a telescope, holding the telescope backwards, the image would be resized down but again the elements of the picture stay the same.

Now if you take that same slide and cut the edges off with scissors, this is known as cropping,but some of the picture elements are now gone. Obviously, the previous resize examples would still work, and would not change the display elements of the now cropped, and therefore different, image. Note that you could get the new displayed images to be exactly the same size as before, by resizing just a little bit more to offset the cropping.

[JeppeK]

Ah okay what aspect ratio do you recommend then? And i dont thing i lost anything of the picture, even though i resized it down.

Ultra-Newbie
Jeppe

[Cornucopia]

It's all about the math. I'll give you the short/easy version:

StoredXresolution/StoredYresolution x Pixel Aspect Ratio = Display Aspect Ratio

You've got 480x576, which is full screen for a PAL SVCD. The PAR for SVCD is ~8:5 (each pixel is much fatter than high). This gives you a DAR of 4:3 (when simplified down).

Now, you want to go to computer file...

Computers use square pixels. That means 1:1 PAR.

You now get to decide what resolution you'll need. Do you want full screen?
(Assume you do, and aren't worried about interlace)
You could go with 800x600, 640x480, etc.
If you want to maintain at least one of the original dimensions, you can reconstruct the other with these equations:

StoredXresolution = DAR / PAR * StoredYresolution

-or-

StoredYresolution = PAR / DAR * StoredXresolution

That gives us:
768x576 (working from one direction), or 480x360 (working from the other)

Since it's better to down-rez than to up-rez. 480x360 is the preferred choice.


Scott

>>>>>
edit:

Notice that both 480x576 in SVCD and 480x360 in DivX/AVI have the same 4:3 Display Aspect Ratio.

edit2:

However, ANYTIME you resize, you'll be doing some type of interpolation and so will be guessing--and losing--something.

[JeppeK]

Okay big thanks man, thats why i dont see the loss its because it is so minimal right?

Sorry if you think my questions are dumb and that they have been answered already but i just want to be sure. And im think im getting it now?

BTW: Is there any calculator that does the the equation you just wrote?

[Baldrick]

Try fitCd

[JeppeK]

Ill try that out tack så mycket Baldrick and thanks all for sticking by my stupid questions

[JeppeK]

Ok heres a small follow up question, is there any way to choose to use VBR when im encoding with Koepis XVID.

[manono]

It's difficult not to use VBR. Either run Single pass->Target quantizer or Two pass->Target whatever, and it's VBR. The only CBR mode is Single pass->Target bitrate.

[junkmalle]

If you need a certain file size use 2-pass and the appropriate bit rate. If you don't need a certain file size and want to assure picture quality use Quantization mode (single pass). Q=2 is nearly identical to the source, even when looking at enlarged still frames. At Q=3 you will see a little macroblocking if you look at enlarged still frames but won't notice at normal playback speed. With Q=4 you will start to notice the macroblocks at normal playback speed if you look closely.

[celtic_druid]

If you want to keep the original res then you can set the DAR/PAR info in the codec config or afterwards via MPEG4Modifier.

The bug where XviD wouldn't resize properly if the encode used bframes that weren't packed was fixed recently to. That reminds me I need to do a new build since the dshow and VfW AR settings were seperated. Previously you are encoding 16:9 so you set the VfW to 16:9 and the dshow decoder would switch from auto to 16:9.

[JeppeK]

What is an appropriate bit rate then? 1200? because i see that the movie sometimes is up to 4000 when i use standard settings.

[Abond]

What is an appropriate bit rate then? 1200? because i see that the movie sometimes is up to 4000 when i use standard settings.

Mainly depend of the file size you want to get.

[JeppeK]

~700MB

[junkmalle]

The appropriate bitrate is... whatever bitrate is required to give you the result you want. Different videos will require different bitrates depending on how much detail is in each frame, how noisy the video is, how much action there is, etc.

If you have to fit a 90 minute video on a 700 MB CD then you may want to use 2-pass VBR with a bitrate around 1000 kbps (keep in mind you need space for the audio too) so you can make a file that's about 700 MB. Use a bitrate calculator to determine the right bitrate.

If you don't care about the exact file size use Quantization mode where you specify the quality you want. Each frame will get whatever number of bits is necessary to achieve that quality.

One word of warning: some set-top DVD/Divx players have problems if the bitrate gets too high. This can happen in Quantization mode at low Q (high quality) values.

[Abond]

~700MB

https://www.videohelp.com/tools?tool=VideoHelp_Bitrate_calculator

[JeppeK]

Thanks Abond really helpful link (thumbs up)
Will but wouldnt a movie seem to lag if i set the bitrate to like 1200 because some scenes uses up to 4000.

[junkmalle]

Will but wouldnt a movie seem to lag if i set the bitrate to like 1200 because some scenes uses up to 4000.

No, the player uses the frame rate to determine how long to show each frame. The only time you will get skips and lags is if the bitrate is so high the player can't read the data off the CD/DVD fast enough to keep up. Unfortunately, there is no way of directly controlling the max bitrate in Xvid (as far as I know). You can only do it indirectly via the Minimum Quantizer settings (Advanced Options, Quantizer).

[celtic_druid]

XviD has DXN profiles which include VBV settings, plus the extra profiles I added for MTK based players which allows for 6000 instead of the 4000 of DXN Home Theatre. This prevents bitrate spikes and caps the max bitrate.

For XviD just enter the filesize rather than bitrate.

[junkmalle]

XviD has DXN profiles which include VBV settings, plus the extra profiles I added for MTK based players which allows for 6000 instead of the 4000 of DXN Home Theatre. This prevents bitrate spikes and caps the max bitrate.

I see the Max Bitrate values on the Level tab of the More Profile@Level dialog. But there's no way to specify this yourself? It says it's "used in two-pass mode". So it's not used in Quantization mode?

One other question: over what period does the limit apply? Each frame? A GOP? A second? Something else?

[celtic_druid]

Nope, no way to specify your self, at least not without playing around with the source. No real reason to either. The DXN profiles are designed for DXN certified devices and I added the 6000 profiles for players that can cope with higher values.

Hardware playback is the only time when VBV really matters and I am not really sure how it would work in quant mode.

There are different limits, like max bitrate, but the limit I think you want is over 1 sec.

[junkmalle]

Thanks Celtic.