when is re-encoding really useful?

[fib0by]

I compared re-encoding (dvd-rb plus HCenc) with a normal requantization software (CloneDVD) for a very large compression factor - video had to be compressed about 50% when going from DVD9 to DVD5, total video duration about 180 min. There was no doubt, re-encoded video looks much better.

But then I compared the two methods for a movie that's 140 min, and the compression from DVD9 to DVD5 is about 70%. The DVD9 source is very good quality. I did an A/B comparison of the re-encoded and the re-quantized video, and no matter what, I could not see any difference. I thought there's more mosquito noise on the re-quantized track a few times, but that might have been wishful thinking.

So, realistically, when it's worth waiting for dvd-rb to re-encode the whole thing? What's the compression factor and the movie duration that constitutes the threshold for you?

[Wombler]

Originally Posted by fib0by

I compared re-encoding (dvd-rb plus HCenc) with a normal requantization software (CloneDVD) for a very large compression factor - video had to be compressed about 50% when going from DVD9 to DVD5, total video duration about 180 min. There was no doubt, re-encoded video looks much better.

But then I compared the two methods for a movie that's 140 min, and the compression from DVD9 to DVD5 is about 70%. The DVD9 source is very good quality. I did an A/B comparison of the re-encoded and the re-quantized video, and no matter what, I could not see any difference. I thought there's more mosquito noise on the re-quantized track a few times, but that might have been wishful thinking.

So, realistically, when it's worth waiting for dvd-rb to re-encode the whole thing? What's the compression factor and the movie duration that constitutes the threshold for you?

There is no answer to that one as it depends on the content of the movie as well as the other factors.

For example if there's a lot of fast moving action (eg 'Saving Private Ryan') then there's less potential to compress regardless of the length of the movie.

Ultimately it depends on how much scope there is for compression as what your results will be like.

Some movies will compress massively with good results.

On the other hand I have a couple of discs at home that are unacceptable quality even after a full re-encode but such discs are very rare in my experience.

Percentage compression is really only a guide as to likely final quality so I wouldn't rely on that too much.

Transcoding is fine where scope for compression is good but the more this is not the case the more a full re-encode becomes desirable.


Wombler

[jdobbs]

It's always better to reencode. End of story. As mentioned, there are some sources (easy to encode ones) where the difference isn't as obvious -- but it is ALWAYS better.

[Wombler]

Originally Posted by jdobbs

It's always better to reencode. End of story. As mentioned, there are some sources (easy to encode ones) where the differnence isn't as obvious -- but it is ALWAYS better.

Absolutely and I run all my movies through DVD Rebuilder although I understand there's some scope for debate when the compression level is only one or two percent.

Some say CCE introduces unnecessary grain and transcoders can do a better job when there's very low compression.

It's a moot point really and very open to individual preference.

I personally have never been unhappy with CCE's output other than with one or two already extremely highly optimised originals where acceptable quality just isn't possible regardless of what method you use.


Wombler

[GrofLuigi]

And there is the "why bother" factor - everyone has to decide for himself on that one (mine is incredibly high).

GL

I'm personally not one for always looking to get the best quality and will trade time saving for quality when encoding to mpeg4. But when it comes to DVD's, since discovering DVD-RB I haven't transcoded a single disc (even with my old system that could only process one disc per night). I simply use DVD-RB and am confident that I'll get the best output possible (short of maybe spending days tweaking filters).

The time I might save doing a test transcode first to check if it gives an acceptable quality just isn't worth it when in a large % of cases I'd end up wanting to re-encode with DVD-RB anyway. I'm sure I'll be glad I've re-encoded too when I upgrade my Monitor/TV and realise that the transcode that looked ok on my old set just doesn't quite compare when viewed on the new bigger one.

A good time to throw a "Thanks jdobbs" out there too

[Video Dude]

Originally Posted by Wombler

Absolutely and I run all my movies through DVD Rebuilder although I understand there's some scope for debate when the compression level is only one or two percent.

I agree about using DVD Rebuilder for everything.

In cases where you have to compress a movie a tiny amount, by a percent or two, use the segment viewer to extract the movie segments and only re-encode the credits.

[Wishbringer]

In times where P3 at 800 MHz were all around I carefulle decided to reencode or just transcode. There was a huge difference between 40 hours reencoding time and 4 hours transcoding time.

Nowadays when dualcores are standard (and overclocked quadcores to 3.8 GHz are not uncommon), there is no discussion needed.
Except maybe you have half an hour time for a movie (thats my actual transcoding time for LotR) and not enough harddrive space to spare.

So I would allways suggest reencoding (maybe including some degrainer/denoiser).

[jdobbs]

Whoah... that's an old processor. Do you have to stand behind that computer and shovel coal into it? I just remembered I have an old 386SX motherboard laying around. I should see how long that one takes. Amazing what has happened in the last few years.

Yeah, I guess there are exceptions to every rule.

[Wombler]

Originally Posted by Video Dude

I agree about using DVD Rebuilder for everything.

In cases where you have to compress a movie a tiny amount, by a percent or two, use the segment viewer to extract the movie segments and only re-encode the credits.

Hey that's a good idea!

Sometimes the simplest ideas are the hardest ones to think of.


Wombler