How exactly does DVD2OneX work?

[DeadLily]

I've been pretty impressed with how little quality is lost. But obviously something has to go in the process. What is it? Is it encryption codes? Resolution? Color depth? What gives? (pun intended)

[noki]

Video bitrate is slashed...as with all transcoders (DVD Shrink, etc)

[AntnyMD]

Actually the bitrate stays the same. The video is analyzed then re-quantized. It basically deletes information it determines to be redundant. This is my understanding, I'm sure I'm leaving something out.

[bugster]

Actually the bitrate stays the same. The video is analyzed then re-quantized. It basically deletes information it determines to be redundant. This is my understanding, I'm sure I'm leaving something out.

If data is removed (which it has to be in orde to reduce the size), then the bitrate is reduced. Its simple arithmetic.

Exactly what data is removed and how this is decided is a completley different question

[AntnyMD]

I'll ask you to check the bitrate of a DVD2OneX processed file where the disc has a lot of content (so that the software will clearly requantize). Check the original against the crunched version with MPEG Info X. You'll see the bitrates are identical.

If it were so simple we would have had these programs years ago.

[galactica]

I always though the frames were being dropped. It was talked about back when the app first came out in here, so maybe a search would yield that post?!?

[deadsierra]

I'll ask you to check the bitrate of a DVD2OneX processed file where the disc has a lot of content (so that the software will clearly requantize). Check the original against the crunched version with MPEG Info X. You'll see the bitrates are identical.

If it were so simple we would have had these programs years ago.

Okay, so the bitrate is a calculation of bits per second. Now, we know that the number of seconds is constant, and if, as you suggest, the number of bits stay the same, then the file size will be the same, due to filesize=bitrate*length. MPEG Info X is wrong. I don't know what it does, but unless the bitrate is changed, you CANNOT change the file size. Even if you change everything else, the file will still be the same size.

Frames are not dropped, because that would screw over anything that isn't a multiscan display (for example, a TV is not a multiscan display) NTSC and PAL DVDs require a specific framerate (29.97 or 25) and they require a specific set of resolutions. the specification allows for a variety of bit rates, which, if lowered, shrink the file size.

Think about it this way; take a constant bitrate file. Say is uses (to be simple) 1 Megabyte per second. That means, if the file is 10 seconds long, the file will be 10 MB in size. if you lower the resolution of the file you don't need to display as much information per second, and then you can lower the bit rate. If you cut down the number of frames per second, you don't need to display as much information per second, and then you can lower the bit rate. Unless you change the bitrate, or the duration of the file, the size WILL NOT CHANGE.

[AntnyMD]

I too thought MPEG Info X was wrong, so I turned on the feature of my DVD player that shows you the bitrate of the video as it plays.

It matched MPEG Info X. Are they both wrong?

[deadsierra]

I too thought MPEG Info X was wrong, so I turned on the feature of my DVD player that shows you the bitrate of the video as it plays.

It matched MPEG Info X. Are they both wrong?

If the bitrate that your dvd player is showing is constant, then probably. Most DVDs are encoded in a variable bit rate. I assume that both MPEG Info X and your DVD Player use the same method to determine what bitrate to show when a variable rate shows up, so they give the same answer. Maybe something in the MPEG header of the file tells them. I'll see what I can find out, then report back.

EDIT: I don't have any DVDs with me right now, could you possibly do something for me? I need the bitrate that MPEG Info X displays for a VOB before compression, and the full size of the DVD. Then, I need the size of the DVD after compression and the bitrate shown be MPEG Info X. The length of the DVD would be nice too. Thanks.

EDIT2: DVD2One explains how they totally misused the words 'Variable' and 'Constant' and shed some light on the issue. (click on the preceding link, its the site you want to go to)

EDIT3: What DVD Player do you have? A bitrate feature is frelling cool.

[maetel99]

I think in doing the requantization, DVD2OneX fails to adjust the bitrate value in each MPEG-2 sequence header to reflect the new rate. It looks like nothing has changed in MPEG Info X, because it just reports the sequence header info, but the data rate really has changed. Otherwise the file size would be the same!

[bugster]

I too thought MPEG Info X was wrong, so I turned on the feature of my DVD player that shows you the bitrate of the video as it plays.

It matched MPEG Info X. Are they both wrong?

It certainly looks that way.
It is simple arithmetic. For the same playing time, you cannot reduce the size of an mpeg without reducing the bitrate.

I am not a Mac user, nor do I have access to one, so I can't comment on what info is being provided to you by the tools you have available. Howver, if you can lay your hands on a PC for a few minutes, take a vob file from a movie both before and after processing with DVD2oneX and drop into bitrate viewer. This actually analyses the data stream rather than relying on file or sequence header info.