True MPEG2 vs MPEG4 comparison

[officerM]

Hi.

Most people seem to be taking a definite quality loss when converting movies from DVD to 1CD or 2CD's. Generally it seems the major loss is in resolution(Gordian Knot slider). Does anyone know, for instance, what a 6GB movie (video only, audio ignored for the moment) would compress to if the resolution was kept the same, and no perceptable quality loss in the image was accepted? Would it be 4GB? 2GB? 5.5GB? I'm really battling, using latest Xvid, to compress a DVD very much at all and maintain DVD resolution and quality - which leaves me wondering if MPEG4 is only better than MPEG2 at low bitrates?

[gitreel]

afaik, the only advantage to using mpeg-4 would be tighter compression, resulting in a smaller filesize.

[teegee420]

The size of the mpeg-2 file isn't really an issue. It could be 6gb or 9gb. What matters is the running length of the movie. As a rule, I never put more than 90-100 minutes of video on an xvid disc. Anything greater than that I will split to two cd's. Plus that way I can keep the original 5.1 AC3 sound(assuming the source has it).

[officerM]

What I mean is - keeping the resolution the same as the DVD, is MPEG4 any better than MPEG2? From what I've gathered myself, there's not much difference between the two, only that free (eg Xvid) MPEG4 codecs are available, whereas MPEG2 is licensed.

This all relates to the argument as to whether MPEG4 type codecs along with DeCSS are really harming the movie industry. Some people (judges for instance) seem to think that a complete DVD can be shrunk down to about 1GB (seeing as the average DVD contains about 6.5 GB in my experience, some the full 9, some only 4). This they argue means that with a broadband connection, DVD piracy over the internet will be rife. I argue back that I have not yet seen a movie squashed down to 1 or even 2GB, even with the 5.1 AC3 downmixed to 2 channel MP3, that looks anywhere near as good as the original DVD. Most people seem to be reducing the resolution - in my opinion, a very drastic loss of quality.

[teegee420]

Ok, if the resolution stays the same I would say that the minimum bitrate necessary would be between 2000-4000kbps, whereas a comparable mpeg-2 bitrate would be between 6000-9000kbps. Frankly, encoding mpeg-4 to a smaller resolution isn't really a problem for me. I don't see a difference as dramatic as you do. It's just a trick to save on bitrate, thereby making the file size smaller.

If you want to see the difference for yourself, try encoding a 1 minute 720x480 clip to xvid using a bitrate of 2000kbps, and the same clip to mpeg-2 using the same bitrate. I think you'll agree that mpeg-4 wins out on this one.

[lordsmurf]

I've never seen good DIVX/XVID files.

I'd love to see one someday, if it can truly exist.

[petar]

What I mean is - keeping the resolution the same as the DVD, is MPEG4 any better than MPEG2? From what I've gathered myself, there's not much difference between the two, only that free (eg Xvid) MPEG4 codecs are available, whereas MPEG2 is licensed.

MPEG4 was designed for low bitrate videos and its application is different from MPEG2. At relatively high bitrates MPEG4 isn't going to give you any better quality than MPEG2 but it can achieve the same quality at a lower bitrate than MPEG2. I'm no expert on MPEG4 (most of my work is DVDs) but I remember I once compared the two at the same resolution and for MPEG2 at 7000 kbps and MPEG4 at 4000 kbps I had to zoom to 400% to tell a difference.

The reason for the poor quality of the divx/xvid files is that the bitrate is too low. Generally these formats are used for sharing videos on the internet or putting a whole movie on a CD hence the bitrate is that low. But if you'd use DVD bitrates you'll get very good quality (though admittedly this is not what MPEG4 was designed for). It's a pity MPEG4 became a standard after DVD. If it was the other way around maybe they were going to include support for MPEG4 and we could have been able to put some 4 hours of full DVD resolution on a single DVDR.

[RabidDog]

I have often wondered at what bitrate mpeg2 &mpeg4 become indistinguishable, I however would put it at a lot lower than 4000k .. I would say somewhere between 1500-3000k, to my eyes, on my 28" Tv. As a good rule of thumb I use 3:1 or 4:1 compression in size ...... .but I always buy books by the pound!!

[Poppa_Meth]

I've never seen good DIVX/XVID files.

I'd love to see one someday, if it can truly exist.

I totally agree here. I've done compression to Xvid and Divx myself and I've seen several other "High Quality" proffesional encodings in the Divx format. I've never ever seen one to equal DVD quality. I've seen a couple that are very close until you start looking at things like running water in a scene. Then you can clearly see the pixilation. I did an Xvid myself, a 90 minute movie to maximum quality came out to almost 2GB and was still not as good as DVD, this viewed on a 20" tv even. with the ease and speed of DVD to DVD backup the ONLY use I see for MP4 would be internet transfer, which 98% of the time would probably be piracy.

[Thorn]

I've never seen good DIVX/XVID files.

The best example I remember was a few starwars promo clips direct from the source. Excellent mpeg4 quality, and also one of the few times I've seen a decent quicktime file

It's all about source. Since so many people use mpeg4 to re-encode some other crap... well you know an mpeg4 re-encode of an mpeg2 can't be as good as the original since you're re-encoding the original artifacts. The only way to get a good comparison is to take original material and encode to mpeg2 and then encode to mpeg4.

In the end I suspect mpeg4 may not quite measure up at high bitrates since it's geared towards better quality at mid-low bitrates (and people try to use it at ultralow bitrates) and doesn't scale up quite as well as mpeg2. As people have said, different applications.

[Suntan]

For those of you "pureists" who can not settle with anything less than a straight copy of the beloved Mpeg2 stream then, no Mpeg4 will never be good enough for you. But please stop spouting off that Mpeg4 is terrible and only useful for horrible copies of obviousely illegal movies. Truth is that rencoding DVD movies, at even a low 2:1 compression with Xvid or Divx give great results.

As for head to head between mpeg2 and mpeg4. When I encode my CG stuff from raw AVI, Mpeg4 always looks better than Mpeg2 for the same bitrate.

-Suntan

[wulf109]

I've just recently started using DIVX(pmeg4). there's no codec that will compress 2.5Gb's down to 700MB's that can maintain "DVD quality". But DIVX comes closer than any available method. Compress a 45 minute TV episode to a 700MB CDR and you come as close as is currently available when viewed on a TV.

[officerM]

I'm with Poppa Meth. After reading about DVD rot (after finding a lot of it in my own collection) - I decided to start getting serious about backing my DVD's up - seeing as the movie studio's are real asses about replacing damaged DVD's. (If they don't want us to use DeCSS, then they could at least replace their own faulty discs!!!)

But I don't want to "backup" my DVD's and reduce them to VHS quality - I would have bought the movie on VHS if that were the case!!! So I started following the guides here and on Doom9 and found that at the settings recommended (2 CD's generally is the target, it seems) I was really not getting the kind of quality that I went out and bought a home theatre system for!!! In my short experience I find I can only comfortably compress a 6GB movie (video and one 5.1 AC3 track) down to 4GB (no recompression of the audio, straight copy). However, and this is the funny part - I tried the same movie with Intervideo's DVD copy software, and it recompressed the whole disc to 4.5GB and it looked the same if not better than the 4GB Xvid. How do they do that??????????????

[satviewer2000]

MPEG4 is to video as MP3 is to audio. It's designed to save space and yet give you reasonable quality video. An MP3 sounds pretty good, but when you listen to it side by side with original CD, then it doesn't sound quite as good. If you watched a DivX encoded movie without watching the original, you would think the DivX movie looks pretty damn good, until you watch it side by side with the original DVD.

What do you expect? You can't compress data 5-10x smaller without losing something. If you want the absolute best quality for a home theatre with a large projection TV, then you have to send it the highest amount of data ... meaning using the original DVD. Even a CloneDVD copy, compressed to a single DVD from the DVD-9 will lose some quality.

And wait until HD-DVDs come out. Have you tried watching the sample WMV-HD files from MS's site? Those will totally blow you away with their breathtaking video quality!