Recompression

[Bobby]

Yup Robert - you're right as usual! I actually went to the step of writing an RW and taking it out to the TV and everything looks fine.

I assume that this indicates that the CODEC is symmetrical. It is re-mapping 0-255 to 16-235 when encoding, but on decoding it maps it back to 0-255. Sounds reasonable. If so there may be some slight compression loss, but nothing major.

[Dave McElderry]

I've been following this thread with interest. I'm glad this ended up being a non-issue. However, there was one small item which Bobby brought up that never got answered. He was talking about the quality slider in the DVD Widescreen preset out of PrEl. Does anyone know what would have been gained/lost by his setting this to 5 instead of the default of 3 that he used?

[Bobby]

Hi Dave.

I tried the slider at '5' and the resultant filesize was the same. But it took a LOT longer to process - so this must be some kind of multi-pass option. I haven't had time to see if I notice any quality difference.

I hope somebody knows the answer.

[RJ Johnston]

The Mainconcept reference manual probably gives a clue as to what the slider does as well as everything else you can adjust.

I believe the slider you mention gives a higher quality image at the expense of longer rendering times.

http://www.mainconcept.com/site/prosume ... 20375.html

[Dave McElderry]

Depending on the playback device, and how critical of an eye you have, the extra time might be worth it. For the average person I would guess that it probably wouldn't make a difference. Mostly I was concerned that it might be creating a larger file size through some kind of interpolation process. I wouldn't be surprised to find that Bobby is correct regarding the multi-pass theory.

[RJ Johnston]

Depending on the playback device, and how critical of an eye you have, the extra time might be worth it. For the average person I would guess that it probably wouldn't make a difference. Mostly I was concerned that it might be creating a larger file size through some kind of interpolation process. I wouldn't be surprised to find that Bobby is correct regarding the multi-pass theory.

The Quality slider does not control multi-pass. There is already a distinctive control for that under the bitrate section: CBR, VBR 1-pass, VBR 2-pass.

[Bobby]

Robert is correct - you can select the number of passes in the bitrate section.

I downloaded and read (briefly!) the referenced manual but it seems to be a reference for a reference application and does not specifically address the Quality slider in the interface to the CODEC that Adobe uses. So if anyone knows what it actually does, please speak up! But very interesting reading - thank you Robert for the pointer.

I did look at a number of the MPEG presets, not just the DVD Widescreen one I was using. The Quality slider exists only in the MPEG CODEC, not the H.264. And it does change, depending on the preset that you select. So I am inclined to leave it as-is, assuming that whoever set it up has selected the correct values for what I am trying to do (i.e. Widescreen DVD).

[RJ Johnston]

Adobe is using the Mainconcept MPEG-2 codec in Premiere Elements.

Edit: When you hover your mouse over the word "Quality" to the left of the slider, there is information about what it does down in the status area at the bottom of the advanced dialog.