DVD2SVCD Problems specific to AVI input

[Nick]

If you have problems with audio sync, or audio/video cut out unexpectedly, try this.
Download VDubMod

* Unpack VDubMod and run it.
* Load your avi file - if you get an error asking about rewriting the header, CLICK NO!!!
* Go to the "VIDEO" menu and select "DIRECT STREAM COPY"
* Go to the "FILE" menu and select "SAVE AS AVI". Select a new filename.
* When VDubMod has saved the AVI, close it and use the new AVI file in DVD2SVCD


If your AVI has mono audio, it will not convert properly in DVD2SVCD - the output will be double speed and sound very high pitched. If this is the case (VDubMod File menu > File information will tell you), then go into Streams menu > Streams list and right-click on the audio stream. Select "Full Processing mode" from the menu that appears. Now right click again and choose Conversion. In the window that opens, select Stereo under the "Channels" heading and click OK. Save the AVI as instructed above and it should now work.

[Nick]

If the process fails with either:
Spumux failed for unknown reasons or
DVDAuthor fails for unkown reasons

You have selected "Do not convert audio" in the audio tab. This option is for AVI's with mp2 or AC3 audio which conforms to DVD Video specifications. If your AVI has audio which is not of a supported format, eg mp3, the process will fail when DVD2SVCD comes to making a DVD out of the encoded video and the untouched audio.

The solution is to uncheck "Do not convert audio" and let DVD2SVCD convert to a supproted format.




f you get an avisynth error "AVISource could not find a decompressor for ...." as long as original file plays OK in Media Player, try this.

NB It only works with Avisynth 2.54 or later.

Open Avisynth.ini (you will find it in your D2S installation folder) in Notepad. Ensure DVD2SVCD is NOT running.

In the Global section of avisynth.ini, replace

AVIReader=AVISource(!filename,audio=false)

with

AVIReader=DirectShowSource(!filename,^framerate,audio=false)

and resave.

Now launch DVD2SVCD, load up your AVI and try a preview.
If it works, do a conversion.

If you get jerky playback from an AVI conversion, the above method may also work for you. Usually this happens if your avi has a "packed bitstream". However, Directshowsource sometimes brings in issues with audio synch in these cases. The best thing to do with such AVI's is use MPEG4Modifier (http://www.moitah.net/download/latest/MPEG4Modifier.zip) to unpack the bitstream prior to conversion.

[Nick]

If your AVI is not resizing properly, get the latest release of DVD2SVCD. Versions 1.2.3 or later have new AVI resizing routines with a "1:1 AR" checkbox in the conversion tab. To help you get the right output for your AVI conversions, I've written a guide to AR's and the new options.

AR's DAR's and PAR's – A quick (!) guide.

OK, first things first, what do these abbreviations stand for?
AR = Aspect Ratio and simply means a ratio of width to height.

DAR = Display Aspect Ratio – for a given video clip the DAR is the width-to-height of the full image, eg 4:3, 16:9

PAR = Pixel Aspect Ratio – Now this is a little more involved. Every digital video clip is a matrix of dots, called pixels. The size of the matrix of this matrix is called Resolution. For example a typical PAL DVD has a resolution of 720x576 pixels. A typical NTSC DVD meanwhile, has a resolution of 720x480 pixels. So, imagine we had the same movie, with 16:9 DAR, both on PAL and NTSC DVD's. Played back on a widescreen TV, we would expect both to look pretty much identical, yet the size of the pixel matrix is very different. The only possible explanation of how two differently sized matrices of pixels can fit on the same size display is that the pixels are of different shape. The ratio of width to height of each individual pixel is known as the Pixel Aspect Ratio, or PAR.

Illustrated examples can be found at http://www.doom9.org/aspectratios.htm


So how does this affect us?

Well DVD uses a video compression standard called MPEG2. All MPEG2 video streams have a DAR flag. Technically this can have 4 settings, but only 2 affect us, these being 4:3 and 16:9.
So, regardless of the resolution of the file, a player able to decode MPEG2 reads what the output DAR is and resizes the file on-the-fly for the output display.

But what if the input video is not precisely 4:3 or precisely 16:9? Some movies are, say 2.35:1. How would you put these on DVD? Well, the answer to that is that black borders are added to the video stream to make the AR meet one of these standards before it is encoded to MPEG2. This process is called Letterboxing.

Now let us take the AVI format. There is no DAR flag and no resolution standard. So an AVI can have a matrix of pixels of any size, yet with no flag to tell the player the correct output DAR. How on earth does that work, then?

Well, set-top disc players which will play AVI files on your TV are a reasonably new concept. In the olden days, AVI files were generally played back on PC's, which generally have a 4:3 monitor. All the display settings in Windows are multiples of 4:3, eg 640x480 (=4:3 x 160) 800x600 (=4:3 x 200) and so on. This means the pixels on a monitor screen are SQUARE – ie width = height, so they have a PAR of 1:1. Since AVI's were normally to be played back on a PC, square pixels are conventianally used. This way, DAR is a simple function of resolution.

Let us take the example of backing up a 4:3 NTSC DVD to AVI.
The input DVD has a resolution of 720x480. This is not a multiple of 4:3. So, if we make a 720x480 AVI, it will not play back correctly in Windows Media Player, which assumes square pixels. However, if we resize it to 640x480, which is a multiple of 4:3 then encode to AVI, it will look fine.

Why, then, you might ask, are square pixels not always used for AVI's? Well, this is because resizing always degrades quality. DV cameras and Analogue Video Captures usually produce files in AVI format. However these files are generally intended for conversion to another format, eg DVD, SVCD etc. So the best way to set about this is to capture your file at a compatible resolution for your final output, eg a PAL DV camera will produce an AVI at 720x576. This can be made straight into a PAL DVD with no resizing, maximising quality.

So, in short, if AVI is the final format, eg DVD to AVI backups, it is usual to use square pixels. However, when AVI is only being used as a temporary format, eg capture AVI's designed to be converted to another format, it is better to make the AVI at the correct resolution for that other format.

Everybody with me so far? If so, you're probably thinking, “All well and good but how does this affect DVD2SVCD?”.

Good question. Well, remember a while back I said AVI's have no DAR flag? This means that if you feed a PAL AVI file of resolution X x Y to DVD2SVCD, it has no way of knowing whether this is for a 4:3 display, a 16:9 display, or is square pixelled and therefore of DAR X:Y. So how does it resize it correctly? Well, the answer is it can't. It used to just resize the AVI to the output resolution. This pleased the capture guys because their input files were designed to fill the frame for the chosen DAR. It wasn't so good for people restoring AVI movie backups to DVD, because their AVI's were not always exactly 4:3 or exactly 16:9 DAR, so this resizing introduced errors and so the output looked wrong. This meant you had to edit the Avisynth script (which does the resizing in DVD2SVCD) to correct it, and for years the FAQ here contained some mind boggling concoction of mathematical formulae that Gerti67 (a former mod here) wrote to resize these files correctly. Then Jsoto (another member here) wrote a little application called AviRes to do the maths for you and in version 1.2.2 Build 3, DVD2SVCD incorporated the AviRes code into his software. Which cheered up movie fans as they could now restore AVI backups to DVDR as a “one-click” process - no need to stop the process part-way in and rewrite the scripts. Unfortunately the camera owners and analogue capturers started making a lot of noise because now they had to edit their scripts!

Confused? Well join the club! So am I, so is the DVD2SVCD author, and so is everyone else! But hopefully this time we've cracked it! As of version 1.2.3 Build 1, if you select AVI input, there is a checkbox in the Conversion tab for 1:1 AR. So you can tell DVD2SVCD whether your AVI has square pixels or not. If you don't check the box, AVI resizing goes back to how it was in version 1.2.1 Build 3 and before. If you check the box, AviRes maths is used to create the resizing parameters.

So, if your AVI DOESN'T have square pixels, as long as the intended DAR is either 4:3 or 16:9 just uncheck the box and it should work fine. Meanwhile if it does have square pixels, check the box and the input file will be letterboxed to 4:3 or 16:9 as per your choice in the dropdown box, using AviRes maths. The only way it can fail is if you have an AVI that is not square-pixel and is designed for a DAR other than 4:3 or 16:9. I cannot imagine why anyone would create such a file in the first place and if you do, and want to use DVD2SVCD to have to convert it, you'll have to do your own maths and edit the Avisynth script. However, I think this version should cover almost every possible scenario.

Here's your new look AR options in AVI mode.

Box NOT checked.

4:3 (no borders, encode as 4:3) – Assumes 4:3 DAR of the AVI regardless of resolution, resizes to fill the DVD or (S)VCD frame, encodes as MPEG 4:3

16:9 (borders added, encode as 4:3) – Assumes 16:9 DAR of the AVI regardless of resolution, resizes to make a letterboxed frame of 4:3 DAR, encodes as MPEG 4:3

Anamorphic (no borders, encode as 16:9) - Assumes 16:9 DAR of the AVI regardless of resolution, resizes to fill the DVD or (S)VCD frame, encodes as MPEG 16:9

Box checked

4:3 (no borders, encode as 4:3) – Ignore this option, it is not actually necessary

16:9 (borders added, encode as 4:3) – Assumes square pixel AVI and therefore calculates DAR from input resolution. Resizes and letterboxes for 4:3 output and encodes as MPEG 4:3

Anamorphic (no borders, encode as 16:9) - Assumes square pixel AVI and therefore calculates DAR from input resolution. Resizes and letterboxes for 16:9 output and encodes as MPEG 16:9

The only proviso to the above options is if you wish to use the AutoFitCD or FACAR plugins, always leave the box UNchecked.