Encode/'Nero Recode' VERSUS trial-and-error for max bitrate

[Allan55]

Hi,

Here's a question that has been bugging me for a while:

Is it better to encode (to MPEG2) at a high bitrate then 'recode' with Nero or your favorite recoder?

Or is it better to use trial-and-error to get the maximum bit rate that will fit the material on a DVD?

I can't see much difference in the tests I've done.

What say you?

Thanks

[DVD_Ripper]

There are some bitrate calcualtors out there that will help you nail the bitrate to allow to fit he most data on your discs .

https://www.videohelp.com/tools?tool=3#comments

[Allan55]

Hi,

There are some bitrate calcualtors out there that will help you nail
the bitrate to allow to fit he most data on your discs .

I forgot to mention that I use VBR exclusively and the calculators I've seen don't really help.

Also, I was hoping to generate some discussion on the trade-offs between the two approaches.

Allan

[iantri]

OK.. you want discussion, here it is:

What you mean by "recoding", I assume is DCT domain transcoding.

This is what DVDShrink, CloneDVD et al. do to reduce the size of DVDs on the fly to put a DVD-9 onto a DVD-5.

AFAIK, the quality must always be lower than if it were reencoded, due to how it works.

While you may not notice the difference if it is a slight drop, you will definately notice the difference if the drop is drastic.. i.e. 5000kbps to 1500kbps.

Due to the rather complicated but clever way MPEG 2 video works it is possible to "re-quantize" video after it has been encoded, which causes the quality to pretty much uniformly drop.. all frames will get blockier.

When it is reencoded at such a low bitrate, you will see a quality drop, of course, but it will be different: Blockiness will increase during motion, but not noticeably during still scenes.

Which encoder are you using? It sounds you are using a CQ (constant quantization/quality) mode, where you set the quantization factor and hope the size comes out acceptable. This is different from what the two most popular encoders (CCE, TMPGEnc) call "VBR", where you specify a minium bitrate, a maximum bitrate and an average bitrate. The total bitrate of the file WILL equal the average bitrate, but will drop or spike as necessary for slow/fast motion scenes.

In that mode, the bitrate calculators work perfectly. The only disadvantage to this mode is that two passes are required (first pass to determine in relative terms the complexity of each scene, and then the second pass to give bitrates that fit the average).

There is no way to accurately predict the output size of a CQ mode.

[adam]

The answer is a definite no. There is no point in encoding high and then transcoding down to the exact size. The quality will universally be lower then if you just encoded to the correct size to begin with. The only use for this method that I can see is if you somehow accidentally miscalculated and went over your target size by a small amount.

As already stated, with 2-pass encoding you can predict your resulting filesize down to the MB so there's no reason to use trial and error unless you do 1-pass VBR. There are ways of running compressibility tests to predict output size with 1 pass encoding, but I'd rather just hit encode and be done with it.

For the absolute best bitrate calculator out there try FitCD, and if you want more advanced features you can buy the full version, Fit2Disk.