Stupid question about the mpeg format

[stream]

This is something I've wondered about for a long time, but have been too afraid to ask. I thought I'd throw it in the newbie section :)

If mpeg2 is a form of video compression, why is it used on DVD's? I thought the point of DVD's is that they aren't compressed. Do I have the completely wrong idea?

-jesse

[txpharoah]

All video is compressed in some form. Yes, even the "uncompressed" video codecs do it. Codec after all, does mean COmpressor/DECompressor.

MPEG2 is the best quality, if done right. (AVI has lots of limits on it, and it's "better quality" is minimal difference at most).

Don't get me wrong, they all have drawbacks, but MPEG2 is a balance of easiest to use, smallest size, and greatest resolution. Although it may not be the BEST in any one category, it is the top choice in most of them, for each item, something other formats cannot claim. Yet.

[bunyip]

Think of this, a 2 hour movie in DVD resolution with no compression would require something like 25 DVD disks to store the video file.

Also the DVD player could not keep up with the amount of Video information it has to process to playback the movie, it would have to drop 25 frames, process 1, drop the next 25 and so on.

Lossy Compression is the only way.

[stream]

Oh. thanks guys ;)

-jesse

[flaninacupboard]

txpharoah
i think -anyone- who works in the video industry would disagree with you. uncompressed AVI certainly does exist, and lossless codecs such as huffyuv exist as well. the difference between an uncomprssed AVI and a DVD (MP:ML) MPEG2 is massive, you're blind if you can't see a difference.
in comparison to AVI MPEG2 is a pain the arse to use. any avi codec -other- than Divx and Xvid is frame accurate, mpeg2 like divx and xvid can only be easily edited at the beggining/end of a GOP. again resolution has nothing to do with it, DVD Mpeg2 is the same resolution as DV, with newer pro DV formats having much higher resolution. filesize is dependant on bitrate, so an Mpeg2 could be higher bitrate than an AVI file or it could be lower.

[bunyip]

I don't dispute that, but we are only referring to fitting a half-decent facimile of the movie on a limited-spaced medium here.

[txpharoah]

Yes, when you get into working with "uncompressed" AVI with dozens of gigabytes, you no longer fit into the audience of this site. That's not what we're after here, plus most of us don't have perfect source to operate from as a studio does. Progressive capture of movies would be great, but we capture tapes and home movies from cameras.

MPEG2 can look perfect on DVD. Until terabyte discs exist, arguments supporting uncompressed AVI are really wasted. One file can fill a system, and quailty differences actually do go unnoticed on current and even some HD tv sets.

But I'll still stick to this: CoDec means Compressor/Decompressor (or Coder/Decoder). In either case, it does reflect some sort of compression. Even photo files are compressed upon save and uncompressed upon playback or reopen. Same can be said for the AVI.

[bugster]

But I'll still stick to this: CoDec means Compressor/Decompressor (or Coder/Decoder). In either case, it does reflect some sort of compression. Even photo files are compressed upon save and uncompressed upon playback or reopen. Same can be said for the AVI.

AVI = Audio Video Interleave.

This is a warpper format and is completeley independant of the actual format of the audio and video data within the file.

As for still Pictures. BMP is either uncompressed or RLE compressed which is lossless. Gif is compressed and alos (I think) lossless. Jpeg is compressed but is lossy.

I agree with you that lossless formats (video, audio or still pictures) are mainly the preserve of the proffesionals, but don't discount them entirley as they do hav their place in the hobby arena, especially audio and stills but even video in some cases.

[Bluez]

i do use huffyuv a lot, even for larger files, it's my standard intermediate format between any conversions / processing etc. going on, right up to the moment i create the final files...

when producing own material, i prefer to end up with a number of independent files, seperated by fadeouts, all huffyuved... then the final run is done by tmpgenc, creating several mpg files

throw them on a vcd, and you have free chapters as well, in a way that is

only for long, large conversions that pass 2 gb i have to go for some compressed format, then i'll always settle for as little loss as possible

in fact, when large creating edited material, i've been using different codecs, often the pegasus mjpeg (not free!) or xvid

my experiences with xvid in this regard have been... diverse (crashes), it's not my preferred codec when EDITING

[txpharoah]

BMP is by far one of the oldest and worst graphic formats, as is GIF. If you want lossless, you move into TIFF, and PSD (proprietary Photoshop) formats so they can hold true 16-bit or greater color. Not aware of anybody that uses RLE for anything. But in all cases, upon save, the elements all become compressed in some form. That's what I'm getting at. Everything on a computer is "compressed," but I guess in your logical sense, you could consider AVI uncompressed, but it still really is compressed, though as shown by it's size, one of the most miniscule compressions. Is it really all that better than MPEG2? Not really. In terms of a perfect video, there are none. Just as there are no perfect "photo quality" digital images. And for the record, I do work in professional arenas of photo and video, and this is the argument most of us make to a relative smaller group that insist it's perfect. The whole myth of always use an AVI should really be thrown away. MPEG2 is the jumping point for future video formats, and AVI has been left long ago. That was the question started by this post. MPEG2 is by far better than AVI because of its abilities and because the quality loss factor of MPEG2 is not too much different than the quality loss factor of AVI. What our future holds is a cross of DV and MPEG2. But for now, MPEG2 was deemed best for the masses. Even where I am, AVI has become abandoned more and more.

[Bluez]

txpharoah, i hate to say it, but even though you appear to be a professional, you got one thing wrong (hey, sometimes one can even learn from an amaatuer )

1. avi is a wrapper format, ie. it does not define what is inside the wrapper, it could contain frames encoded in mpeg2 fashion with an alternative gop structure (i only)... on top of that, uncompressed avi exists, it all depends on the codec being used

2. on middle level systems (most nle's window based, up to premiere / media studio and even some of the higher level systems) that are using windows (ah, there's the catch ) the avi format is quite often used for editing, especially with source material coming from dv, dvcam, dvpro etc.

3. mpeg2 is quite a nice format for transport or end products but it's quite hopeless for editing, unless you go for i only gop structures, or you use systems that preload a few frames (more and more 'cheaper' nle's do that these days)

4. mpeg2 is NOT better than other codecs, it's just different, if it's not real time i love mpeg2, if its real time, then what you need is expensive hardware... (especially with multiple sources multiple effects)

i can't say anything about the format on macs though, the situation there might be different

hope you don't mind my comment

[txpharoah]

Don't mind comments at all, this is a place of teaching and learning.

But the AVI (we call them container files at work, but yes, wrapper is the technical definition) is only as good as the codec. The HuffyUV is in reality not an uncompressed format. Good compression, yes, but not truly uncompressed. You've got to look at its algorithms to understand that part. It works much in the same way as a zip file. It may be "uncompressed" when viewed initially, but it does get compressed in storage, and as zip files do, is very succeptable to areas that go bad from over compression and areas that cannot be properly uncompressed after the compression happened. The HuffyUV is more problematic than the zip format, unfortunately, as zips have had more developers to improve it over the years. The algorithms are similar to some extent too, hence my zip file analogy.

But to address the question by the newbie, I'll give you a personal example: I shoot lots of photos, and am a professional photographer in addition to my pro video work. When people ask me what would be best as a digital photo, they don't want to know my real answer. They want to know what is best for them. The real answer would be to use a Nikon D1 or better camera, in raw mode, with 16-bit color, saved as a 16-bit PSD Photoshop file, use a few filters, and shoot proper exposures to begin with. But that won't work. Why would I try to tax them with a complex file that is too large for emailing friends or printing to most printers, and uses a camera so expensive it would outprice their car? My use is not home use. Mine is to publish in a magazine (and even then Sports Illustrated and National Geographic will only allow film, not digital, not yet).

The answer for them would be to use a minimum 1 MegaPix camera, and save to JPEG. Then they only have two questions: how to print good, or how to email fast. Both of course, are just image size and DPI settings. And they're happy. That applies to 99% of the audience all the time.

Same can be said about this newbie question. Can AVI and all that jazz be better. Well, maybe, but not in practice for 99% of the people in almost all situations. Even that final 1% is having arguments over it. MPEG is the answer here, and it brings back only two questions again: CD quality or DVD quality? Anything more, much like my photos, would go unnnoticed. And some video uses, much like my photo film, must stay high-definition tape or film, because once again: not good enough, not yet.

Also, you did a good job of identifying something. If you want to edit an MPEG2, capture pure I frame, then after edit, save back to a standard IPB format. That does work quite well, and is much smaller and faster than the AVI headache.

Realtime encoding is what they use at DirecTV and Dish Network. Satellite streams MPEG2 files to you, and many people recognize satellite tv as one of the best video sources. Is the realtime hardware more expensive? Yes, somewhat, but it won't break the bank. You really do get what you pay for in the video and photo world. Capturing with a realtime MPEG2 encoder like the ATI cards out there, then a dump to DVD or first re-encode to a more final MPEG1 or MPEG2 file works great, and is what I use at home for restoring old home movies and other tapes.

[Bluez]

txpharoah, you brought up one interesting thing: how lossless is huffyuv? did anybody ever test that? i know that converting to yuv definitely means loss, but when using it in rgb mode, does it create losses as well?

i've been using lossless mjpeg in the past, but it turned out to be too slow, and have been somewhat reluctant to use the different dv codecs, i would preferr to stick with lossless compression all the way

if huffyuv is not lossless, what are the alternatives?