What iDVD '08 Compression Options Really Mean

Aug 15, '08 07:30:00AM

Contributed by: withdave

Every time I've used iDVD '08 and reached the point of checking the Project Info pane's Encoding options, they never make complete sense, even after searching the web for answers. I'm in the process of transferring my Laserdiscs to DVDs and have now built up enough experience that I think I've figured this all out. Here's what seems to be going on.

The gist of the confusion about encoding is that the word "quality" is used in two different ways. There is the quality of the rendered video to be burned on the DVD, which is really what is important. But, unfortunately, the word quality also appears in the naming of the compression algorithms used, Best Quality and Professional Quality. This latter use is ill-advised, because the amount of compression applied to your video may or may not affect the quality of the video you end up with.

We all understand the meaning of picture quality, and iDVD '08 usefully indicates final DVD video quality via a color grading scale, from green to yellow to red. Green indicates excellent DVD quality and as the color goes away from green the resulting quality is less. Just as beauty is in the eye of the beholder, a video quality level that is not green may still look good to you and be completely acceptable. The only way to tell is to burn a DVD with such levels and examine things for yourself.

Now lets talk about the video encoding (compression) quality level. To eliminate the point of confusion between compression and picture quality it is better to think of the encoding options as follows: Best Performance is Low Compression Encoding; High Quality is High Compression Encoding; and Professional Quality is Very High Compression Encoding. The higher the compression the longer the required rendering time but the smaller the resulting files.

Best Performance encoding is the fastest of the three but requires the most DVD space to hold the rendered result. A unique feature of Best Performance is that it only produces the excellent (pure green) level of video quality. Unlike the other two encoding options, which we'll go into later, a given video content processed by Best Performance always produces the same fixed amount of output. Because of this, when you have Best Performance chosen, the final burn image will either fit on your target DVD size or it won't, and always shows up as having a solid green quality level. Depending upon my project's movies, menus and slideshows, I've found that somewhere between 70 to 90 minutes of material will fit on a 120 minute DVD.

Since Best Performance encoding always gives excellent video quality and is fastest, you should always try using that setting first in your DVD projects. If your material doesn't fit using this encoding then you have two choices: reduce your material or use one of the two higher but slower compression levels to fit your content on the target DVD. If Best Performance yields a render size just a little too big to fit, you can try minor things to trim your content such as changing button frame movie clips to still frames or eliminating button frames altogether. Sometimes, just by changing a few movie clip buttons to still frame buttons I manage to get enough space trimmed to fit everything on my target DVD using fastest Best Performance compression.

If you need to fit more material on your DVD than what Best Performance can handle, then you must go to a higher level of compression. The other two encoding options are different from Best Performance in that they are able to modify their compression levels, within limits, so that the final rendered video fits onto your DVD. However, the more they have to compress to accomplish this, the poorer the video quality will be, as is shown by the Project Info pane color quality bar.

High Quality encoding (think of it instead as High Compression) doesn't do as much work as Professional Quality encoding (Very High Compression) and for this reason it can't shrink your final rendered output size as much as the latter before video quality starts to weaken. Profession Quality compression does more work and takes longer but produces smaller output files that are still in the green video quality level. Professional Quality compression can take twice as long as High Quality compression. If High Quality compression doesn't reach the color quality level you want then you have no choice but to use the Professional Quality compression encoder and take the much longer render time hit or split your content up onto more than one DVD so you can use a faster encoder.

My Mac Mini Core 2 Duo renders a single layer DVD using Best Performance compression in 1 hour, Best Quality compression in 6 hours and Professional Quality compression in 12 hours, so you can bet I try to use Best Performance if at all possible.

To summarize: If Best Performance encoding can fit all your material into your target DVD size then use it because the result will be high quality video rendered in the fastest time. Otherwise, you will have to trim some of your content so Best Performance can fit it in or try using the next more powerful option of High Quality compression. If High Quality compression doesn't compress your content with a good enough quality line color level, then you have no choice but to use Professional Quality compression or split your DVD project up into two DVD projects and burn two DVDs.

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