Saving Space: 16:9 -> 4:3

[outsideAG]

In making DVD backups I personally prefer to keep as many extras as possible, and as a result, I have to make some quality trade offs in the process.

One method that I have used is to resize the 16:9 anamorphic feature to 4:3 LBX. This isn't something that I have ever seen written up before, but at least as I understand it, this would reduce the number of active pixels being encoded by 25%, and thus yield the same quality with a (not quite, but close to) 25% lower bit rate.

The only downside of this method would be a loss of resolution on 16:9 displays. I don't have a 16:9 display, and I probably won't have one any time soon, so this is fine for me. I would rather have special features on my backup than picture quality I can't even see.

1) Am I right in thinking that this is a good way to make backups? Since I haven't seen this recommended in any guides, I wonder if I am missing something, and this isn't actually a good space saving method.

2) If this is something useful, then I would like to recommend it for DVD-RB. Currently, I can do it myself by manually editing the ecl and avs files, and using IfoEdit, but this is a pain. If this feature would be useful to others, (i assume) it should not be that hard to add to RB.

[jdobbs]

Here's the problem:

as I understand it, this would reduce the number of active pixels being encoded by 25%, and thus yield the same quality with a (not quite, but close to) 25% lower bit rate Yes it would reduce the number of active pixels the "true" size of your output would be 720x360 rather than 720x480 (assuming NTSC). That is offset a little by the fact that you will be encoding the black bars at the top and the bottom. I think the error in this reasoning is the believe that you will lose nothing in quality. In fact the quality is also reduced by 25%, and you can never get it back by resizing upward... Losing quality is one of those things DVD-RB is trying to avoid.

This certainly works... but isn't recommended. In fact a much more common practice is to do the exact opposite and take a source that was originally 4:3 letterbox and convert it to anamorphic 16:9.

[outsideAG]

Yes, it definitely does reduce quality, but only if you are watching it on a 16:9 display.

On a 4:3 standard def display you end up loosing that extra 25% anyway because the DVD player does a vertical scale on the frame in order to display it at the correct AR.

My point is that, if I will never be watching a backup on a 16:9 display, then I am just wasting that extra bitrate encoding information that will be tossed out by my DVD player at playback time anyway.

[jdobbs]

I guess we'll just have to disagree and leave it at that. :)

[outsideAG]

Fair enough.