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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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