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What iDVD '08 Compression Options Really Mean Apps
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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What iDVD '08 Compression Options Really Mean
Authored by: altotus on Aug 15, '08 08:59:02AM

Er. Best performance is constant-bitrate encoding with a slightly diminished bit-rate. High-quality and Professional-quality use variable bit-rate encoding with a slightly higher average bit-rate, but they also (appear to) use different quantization and even multi-pass encoding. They are not "high compression" and "higher compression" at all.

Depending on how you look at it, iDVD fortunately or unfortunately doesn't give you a whole lot of information about the encoding. You don't know home many I/B/P frames there are, what quantiziation matrix is used, the motion-prediciton, etc. Some of that you can learn after the fact using things like VLC and ffmpeg (but most of the encoding parameters simply can't be derived from the video).

My experience so far is that both the High-quality and Professional quality modes make a number of presumptions about the quality and nature of the video and used parameters based on those assumptions. The net result is that sometimes you get better looking results, sometimes you get worse. I do have one stand-alone Samsung (DVD1080P) player that seems to stutter on some of the Professional quality output, and it looks as though the VBR encoding is peaking with bit-rates just at the edge of what the player can handle. I haven't had time to check if the peak is out of bounds for the DVD spec yet.

For such a simplisitic app, iDVD works pretty well, but it would be nice if there were an "Advanced" mode that allowed at least a little tweaking of the encoding (setting number of passes, bitrates (max, min, and average), etc.).

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Secret iDVD advanced mode option...
Authored by: gabester on Aug 15, '08 01:38:06PM

Apple has already implemented this. I think you need to edit this plist:


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Secret iDVD advanced mode option...
Authored by: drmacnut on Aug 16, '08 12:40:56AM

"Apple has already implemented this. I think you need to edit this plist:" - Gabester

I know it's off-topic to say so, but, Gabester, that was really funny! Good one!

On topic, I just wanted to say thank you to withdave for both taking the time to analyze his own workflow and to write this article. Compressing video for DVD using iDVD is, as we all know, not necessarily the best route, but getting into Compressor, Cleaner, and their ilk is not easy to do. For the most part, iDVD makes the cut, and I also use it here locally to produce final output for our FCP Studio-edited videos.

I always try to use the least amount of compression possible on my own iDVD projects, as I agree that sitting around for 6 to 12 hours while video renders --all the while risking the fateful and all-too-frequent crash half way through!-- is not fun at all. With that in mind, I have taken to always producing a burnable image of the video, which I have iDVD create and save on my hard drive of choice. After that, I can make as many copies as I like, and don't have to worry about hangs, coasters, underruns, etc, nor do I have to keep the original rendered iDVD project file just to make future copies, which eats up loads of HD space besides. I don't use iDVD to actually burn anything (Disk Utility does that for me).

Anyway, thanks again, withdave. Take care, everyone.

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What iDVD '08 Compression Options Really Mean
Authored by: withdave on Aug 15, '08 05:17:33PM

I used the compression term because all DVD videos are stored as MPEG2 compressed format and the relationship between the various codecs operates in an analogous fashion to compression. Yes, in pure terms it would be more accurate to use a phrase like 'optimal bit-rate' instead of 'compression', but the every-day iDVD user is likely to be familiar with zip files and the like. The higher iDVD '08 encoders yield smaller files with the same quality. Even though they are not intending to explicitly do compression, that is the result. Professional Quality fits my 2 hours (8 Gigabytes) of input video onto a single layer DVD, whereas Best Quality can only fit 70 to 90 minutes worth.

My experience using iDVD '08 is not extensive, but the impressions I get of its encoder tradeoffs fit with the remainder of your comments.

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What iDVD '08 Compression Options Really Mean
Authored by: Anonymous on Aug 19, '08 10:36:05AM
I don't understand why you're apologizing for referring to a lossy compression technique as "compression".

If you want more control over iDVD, just remember that iDVD is to Final Cut as iPhoto is to Aperture.

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