How lossless is lossless...?

[comomolo]

I'm in the process of archiving my DVDs. I ran across this CQ-Lossless profile in MeGUI and I wonder what exactly does it mean? Will it leave the image quality of the original movie intact? What does it mean otherwise?

Thanks.

PS: No need to say I'm a total noob...

[Kurth]

http://en.wikipedia.org/wiki/Lossless

It is a way to compress the most that you can without losing any detail the result is a movie with the same quality as the source but with less file size.

Instead of using LossLess encode I prefer to use 2-Pass encode to make a movie with 2240MB soo I cant put two movies inside a DVD-5 with an incredible quality.

[comomolo]

I understand that, but I'm puzzled by the many profiles in MeGUI. Should I asume this is the highest quality one since it's lossless? If I don't care about file size when transcoding from DVDs, this profile will give me the EXACT picture quality found in the original DVD? May I expect it to be better, then, than MPEG2 transcoding from DVD9 to DVD5?

Sorry for the many questions. I find it hard to believe that I can get the exact same quality of the original DVD at a third of the size. This would be the holy grail I've been looking for lately... :)

[Sharktooth]

Lossless means without quality loss (except from the colorspace conversion, if needed), but it will be probably much bigger than the source since it is already compressed with a lossy encoder.

[comomolo]

Sorry Sharktooth but I don't get your reasoning. I know that trying to compress losslessly a pure noise image will make it actually bigger, but I don't think an image with a few compression artifacts on it (as one picture from an MPEG2 movie) can be put in the same category as pure noise.

I'm testing the CQ-lossless profile in MeGUI and it's giving me one third of the original movie so far (I'll confirm when it's finished).

Also, what colorspace conversion are you talking about? Aren't the MPEG2 in the DVD and x264 using the same colorspace?

[Audionut]

Sharktooth is not saying "you" will experience color space conversion. Read his statement again.
Lossless means "no" quality loss. <== Unless there is a color space conversion).

If you are encoding to lossless from an mpeg2 source, the resulting lossless file will be larger. <== Unless the original mpeg2 source was encoded at a huge bitrate and/or you are applying processing to the video before encoding to lossless.

[Eleo]

I question this concept of "lossless"-ness since a DVD is already not as good-looking as its source material, film. Even in a digital-to-digital conversion like the last two Star Wars films, isn't the quality not as great as it could be or will be with HD-DVD/Blu Ray? Just asking.

I like the concept of "archiving" stuff and just being able to chill knowing that it's timeless but it doesn't seem quite yet possible :(

[SeeMoreDigital]

Hmmmm!

If you don't want to suffer "any" quality loss from your orignal DVD sources. Have you considered using say, DVD Decrypter or DVD Shrink to back-up them up as ISO (image) files?

[vlada]

@comomolo> I hope this helps you to understand the problem:

Let's assume I have a 2 hour PAL movie 720x576@25fps. If it was uncompressed, every pixel would use 24bits (RGB24) = 3 bytes. Now both MPEG-2 (DVD) and MPEG-4 (XviD, x264) typically YV12 (4:2:0) colorspace. It means that on 4 pixels I will have 4 bytes of luma and 2 bytes of chroma. So Instead of 12 bytes I will only need 6 bytes, 1.5 byte per pixel. I hope my calculations are right and clear so far.

Now we have a picture resolution 720x576=414720 and there are 25 of them in one second. So to store a second of uncompressed movie I need 414720x25x1.5 = 15,552,000 B (cca. 15 MB). To store 2 hours I need 104 GB.

A typical DL DVD would have a picture compressed to 5GB, the rest are usually bonuses and sounds. So we have a 20:1 compression ratio on a DVD.

Lossless video codecs usually compress a picture with ratio of 1:3. This means that x264 lossless video will have about 35GB. There will be no quality loss compared to the original DVD. But it will be 7x bigger. Do you still think it makes sense to compress a DVD with lossless setting?

I assume you know, that a codec always works with uncompressed data only and that it can't know if the original source was compressed or not. So you'll get the same results out of it no matter how the source was compressed.

[mod]

In other words, it makes no sense to encode lossless something that has already been compressed lossy, unless you have to edit it..

[comomolo]

@vlada: Yep. I understand it. I was hoping that "lossless" would refer just to intra-frame information, and that compression would come from some inter-frame compression magic in H.264. Your calculations seem right to me. However, many of my movies aren't 5 GB but something like 7~8 GB (yes, just the main movie, without the extras).

I woke up this morning and saw that my movie had "compressed" to 23 GB... Because the figure in MeGUI has no thousands separation coma I was "seeing" 2,3 GB. :(

I can't "archive" the full ISO image of the original DVD. I don't have that much disc space. (I'm trying to fit some 400 movies in 1 TB, meaning I have a maximum of 2,5 GB per movie, and less would be nice, since my collection should be growing.) IMO, the original MPEG2 quality of most DVDs isn't that great, so loosing quality from there is not nice.

I guess I'll start trying different compression schemes to see if any of them gives me visually the same picture. I'm going to watch my movies "zoomed" to a 1920 pixels wide picture. If I can't tell the difference from the original at that size, I'll be happy. I'm very picky though...

Your suggestions for using any of the MeGUI presets for that goal are very welcome.

CM

[Sharktooth]

HQ-Slow or HQ-Slower if encoding time is not so important.

[comomolo]

Thanks Sharktooth. I'm already trying HQ-insane. As you can see, time is not important... ;-) I've put 3000 in the bitrate box. Will that be enough not to worry about bitrate ever again? (I'm lazy...)

Also, what about your AVC matrices? Are they already included in these presets or should I download them?

[foxyshadis]

There is a bitrate calculator in megui for a reason.

Lossless is for editing and audiophiles, period. (Editing includes encoding some of those horribly slow avisynth scripts, only doing it once helps.)

Custom matrices are less important in AVC than ASP, so they aren't included in the presets, but I think they're distributed in the the megui package somewhere? If not, maybe they should be... though that might encourage people to use them unnecessarily.

[Audionut]

400 movies at 1.5 hrs each with 448kbs ac3 = approx bitrate 3300kbps.

[Sharktooth]

3000kbps should be enough to have "transparent" backups.

[vrpatilisl]

hi
i am new here, can any body tell any preset 100% transparent to DVD like when we rip audio CD to flac. as flac is 100 % lossless.
thanxs

[vrpatilisl]

for comomolo

i think making iso of dvd is good option. when any new container or format come in future with much compression and more quality. then it will work.

[Audionut]

5yr thread bump ftw.

Comomolo is also no longer registered here.

[AMED]

hi
i am new here, can any body tell any preset 100% transparent to DVD like when we rip audio CD to flac. as flac is 100 % lossless.
thanxsBest thing to go is not re-encode it again. Rip the DVD with MakeMKV (http://makemkv.com/) and it will copy the titles and audio you select in to a .mkv file with no loss in quality.