AutoGK Vob --> XVid file sizes query

[djdust]

Hi all

I wonder if anyone can help me. I've been using AutoGK for as long as I can remember to convert VOB files that I've ripped from DVD into Xvid files. When converting, I set the "Target Quality" to 100%. In most cases, I end up with files that are smaller than the original VOBs (sometimes a fraction of the original size), yet, occasionally, I end up with files that are much larger.

I don't understand how this happens, I'd have thought that the size would be about the same in every case. Can someone explain what happens in this process? Is any compression / decompression happening at all?

Thanks in advance

[LigH.de]

The more details the video contains, the more bitrate is required to reconstruct it conveniently. And "details" are not only interesting structure. They can also be uninteresting noise (or even worse, intended grain). Or "combing" due to interlacing or hard NTSC Telecine (especially with much motion). And even compression artifacts caused by low quality encoding on the DVD, which would have to be recreated by Xvid.

Furthermore, the more motion is present, the harder it can be for a codec to find similarities to use to spare bitrate; clean still scenes can be compressed a lot tighter than fast action scenes.

Every movie is different. Every movie has to be handled in a slightly different way to compress it optimally.

[djdust]

Thanks for the quick reply. To clarify though, is the picture quality *exactly* the same, frame-by-frame?

[LigH.de]

Certainly not. (BTW: There is not even a metric which can measure "picture quality" objectively, quality is a subjective concept, depends on each individual member of the audience.)

On one hand, there is a difference of quantization factors between I, P, and B frames. That's on purpose, it is useful and hard to recognize.

On the other hand, Xvid does not implement any technique controlling the quantization in relation to the degree of quality loss (like the CRF mode in x264), only a constant quantization (1 pass) or an attenuated quantization (2 passes). For the available techniques to optimize the bitrate distribution, a 2-pass encoding achieves a more or less stable quality during one movie, but it's hard to rate the loss among several different movies.

If you encode a video with combing in progressive mode, you will have a certain quality loss despite a much higher bitrate.

[djdust]

Fair enough, I guess my next question is..... seeing as AutoGK is getting more and more unstable as the years go, is there a better tool to convert VOB files (Handbrake maybe)? I need to retain as much quality as possible (even though I appreciate there's already compression on the files) and, ideally want to be able to play them in the future from an iPad, something I can't currently do with Xvids.

[hello_hello]

Try MeGUI. It can be less "auto" than AutoGK, but it uses many of the same tools to do the work so it might be a bit familiar in that sense. It also has a OneClick encoder that'll automatically crop and resize etc amd it'll batch encode, although I've pretty much never used it myself.

MeGUI supports xvid, x264 and x265 encoding, x264 being the successor to Xvid (and much better) and x265 the successor to x264 (although it's still in development and hardware decoding support is far less common at the moment).

StaxRip is Avisynth based and actively developed.

If you want a GUI with many inbuilt functions such as Avisynth filters that most other GUIs don't supply (although you can generally add them yourself), Hybrid has options for days.

Handbrake is not Avisynth based but it's designed for ease of use and supports x264 and x265 encoding. Vidcoder is an alternative Handbrake GUI.

[djdust]

Thanks. Will all of these also allow conversion of my existing Xvid files to a format that'll work on an iPad? Again, I don't want to lose any quality...

[LigH.de]

You will always lose quality when converting with any lossy method. But the loss may be so little that you don't recognize it easily.

And when you convert an already recompressed copy again, you will lose even more quality than if you converted from the original source.

For an iPad as target device, you should be able to use x264 as encoder. You just need to limit the complexity to a specific AVC Profile@Level, depending on the pad's chip generation, and when multiplexing to the recommended MP4 container, a specific tag may have to be added to make it appear compatible to iTunes (MeGUI supports that, not sure about other tools). The result should most probably have a better quality than Xvid when done correctly, and from the original source.

[djdust]

You will always lose quality when converting with any lossy method. But the loss may be so little that you don't recognize it easily.

And when you convert an already recompressed copy again, you will lose even more quality than if you converted from the original source.

For an iPad as target device, you should be able to use x264 as encoder. You just need to limit the complexity to a specific AVC Profile@Level, depending on the pad's chip generation, and when multiplexing to the recommended MP4 container, a specific tag may have to be added to make it appear compatible to iTunes (MeGUI supports that, not sure about other tools). The result should most probably have a better quality than Xvid when done correctly, and from the original source.

Is it possible to remux rather then recode? With my Xvid's, I've already converted them from VOB's so don't want to lose any more quality if at all possible (the original source is long lost). Or do files *have* to be re-encoded to x264 to make them work on devices?

Sorry for all the probably-stupid questions, am very very rusty about all this stuff..

[LigH.de]

VOBs contain MPEG-2 video.

Xvid is an encoder which produces MPEG-4 Part 2 video (ASP).

x264 is an encoder which produces MPEG-4 Part 10 video (AVC). This is something different. Like must (original in the DVD studio), wine (MPEG-2 on DVD), liqueur (ASP by Xvid) and brandy (AVC by x264).

[djdust]

So... to clarify my understanding... If I want to convert my archived ASP (Xvid) files into a more modern format, I need to use X264 (which is not a file format as such but a means of encoding) to convert them into AVC? Does that then go into a "container" like MP4?

[LigH.de]

Previously, you converted your DVDs to MPEG-4 ASP in the AVI container, using the Xvid encoder.

In the future, you may convert your DVDs to MPEG-4 AVC in the MP4 container, using the x264 encoder.

But converting your already existing ASP (Xvid) AVIs further to AVC (x264) MP4s would be a waste of efforts. Either keep them as they are, or convert your DVDs again. But converting your archived videos will only result in a quality worse than your copy, every lossy conversion will reduce the quality further.

[djdust]

I'd be happy to leave my already existing ASP (Xvid) AVIs as they are if it wasn't for the fact that, at some point in the future, I want to import them into iTunes so I can sync them to an iPad. I tried it some time ago and the format wasn't recognised. Is a conversion (and thus more quality loss) the only way to do it?

[LigH.de]

Yes. If the current format is unsupported by your playback device, you must convert to a format your playback device supports (or install a different player which supports more formats, but I don't know which other players Apple allows besides its own iTunes).

It would be preferable to convert from your DVDs again. If that is not easily possible, you can only try to convert your Xvid AVIs with as little further loss as possible (even if this result might become larger). The encoder x264 has the CRF mode which will try to keep the quality loss below a certain threshold. Many people are satisfied with a CRF value which is below 20 (often in the range 18...15, depending on your demands; smaller value means smaller loss, but larger result).

[djdust]

Ok, thanks for all the replies. Really helpful. I'll do some experimenting and see how I get on..

I've also got a similar query related to the audio side of things... Some of the Xvid files I have retain the original AC3 files from the DVDs they came from as, I used to play music videos in a nightclub and thus wanted to avoid any degradation whatsoever in sound quality. Is there a way to still keep them intact if converting to an iPad-friendly format or is a degree of conversion once again inevitable?

[hello_hello]

I don't own an iAnything, but surely there's a third partly player that supports a wider range of formats than standard?

Consulting Google indicates this will solve the problem.
https://itunes.apple.com/au/app/vlc-for-mobile/id650377962?mt=8

I don't know anything about iTunes, but surely there's got to be a way to transfer AVIs to an ipad?

Edit: I've only vaguely heard about Apple and AC3 support. It seems you have to pay licensing fees to decode AC3 on Apple devices. Unbelievable. Even VLC won't decode it. There's no doubt a player out there that will even if there's no longer any free options.

[djdust]

I don't own an iAnything, but surely there's a third partly player that supports a wider range of formats than standard?

Consulting Google indicates this will solve the problem.
https://itunes.apple.com/au/app/vlc-for-mobile/id650377962?mt=8

I don't know anything about iTunes, but surely there's got to be a way to transfer AVIs to an ipad?

Edit: I've only vaguely heard about Apple and AC3 support. It seems you have to pay licensing fees to decode AC3 on Apple devices. Unbelievable. Even VLC won't decode it. There's no doubt a player out there that will even if there's no longer any free options.

Just given VLC a go on the iPad and, sure enough, AC3 files come come out silent and display a copyright notice. Plus. a bit of digging also reveals that using VLC will drain the battery more quickly as it uses a lot more processing power. Also, it seem that any apps out there that *do* play AC3 will no doubt stop doing so at some point once they get hit by a potential lawsuit.

So, at this point, it's looking like VLC is a no-no and I might as well try to stick within the constraints of iTunes if I want to be using the iPad, i.e. x264-encoded MP4 conversions of everything I have - video and audio wise... Let's be honest, they're DVD-quality anyway so fuzziness comes with the territory anyway.