Adjust bitrate or use DVD Shrink?

[NIIDeep]

Hello All,

I'm in the process of converting VHS tapes to DVD. The video footage I have is at least 2.5 hrs.+ per tape and I've pretty much committed to a 1:1 conversion, i.e. 1 VHS tape for 1 DVD. I'm trying to make this simple, nothing fancy. Capping with ATI AIW and authoring in DVD-Lab.

With DVD there's the 4.7/4.38GB space limit and depending on what my bitrate is, I sometimes have MPEG2 files greater than 4.38GB, depending on the original VHS video length. I then re-cap with an adjusted bitrate and sometimes I fall way below the 4.38GB limit. It's been a huge guessing game and I'm wasting alot of time on this. I want to maximize on quality, i.e. have ~4GB MPEG2 files.

So my question is it better to just settle on one bitrate, cap it, author it even though it exceeds the DVD size and then shrink with DVD Shrink to fit? Or shall I continue with my guessing game.

I think I know the answer but would like to know any Cons with using DVD Shrink.

Thanks.

[mats.hogberg]

It's always better to encode at the right bitrate. And there's no guesswork involved - really just simple maths. And bitrate calculators to help you on your way.

/Mats

[NIIDeep]

Well... from my experience so far, the calculated value is not an absolute value. It seems more of an estimation and I believe there is a high dependency on the video content.

For example, for a 2hr. 51 min. video to be encoded into MPEG2 to fit on 1 DVD with 256 kbs audio, it recommends a bit rate (assuming CBR) of 3.3 Mbs. However, I just encoded this video at 3.6 Mbs CBR yielding a MPEG2 file of 3.5 Gb. According to the calculated with my higher than recommended bitrate, I should have a file size exceeding 4480 KB. But I didn't.

I "could" go with what I have but I have about 800 MB of room left on the DVD that could be used to increase the quality of the video. Granted it may be negligible but every little bit counts for me.

From what I've seen the bitrate calculators are just ballpark figures to give you an idea of what values to start out with. There's room for optimization.

[mats.hogberg]

Calcs are pure science - simple maths. Encoders are however not all equally good at arraiving at the set bit rate. But arriving 800 MB (~20%!) from the desired target has never happened to me, regardless of encoder and encoding method used.

/Mats

[SaSi]

2 hours and 51 minutes encoded at 3.6Mbps cannot give a 3.5 Gb result. It appears that your encoder is not encoding correctly for this average bitrate.

Which encoder are you using?

In case you miss the DVDR capacity by a few Mb, then it is much better to re-encode with DVD-Shrink than re-encode and re-author the whole thing. However, even for 50-100Mb reduction in size, you must do a Deep analysis and enable version 3.2 quality enhancement otherwise you will get sporadic macroblocks visible throughout the video.

[NIIDeep]

I agree, I should not have had a 3.5GB file for a bitrate of 3.6 Mbs. It "should" should have been closer to 4 GB file.

Maybe I should clarify..

I'm using a H/W encoder rather than a S/W encoder (like TMPGEnc) via the ATI AIW encoder chip. Encoding is done in real time. I'm using MMC 9.03 and set a bitrate of 3.6 CBR. Perhaps it's an issue with ATI s/w?

[Baldrick]

encoding is not authoring. moving you.