AMV size

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Postby AbsoluteDestiny » Thu Oct 03, 2002 6:05 pm

You should never do colourspace conversions. If you think that there is no real loss then you might find this interesting.

If I use HuffYUV in YUY2 mode for each coversion and did as follows:

- Ripped a dvd and made HuffYUV clips in virtualdub in Full Compression mode
- Edited in Premiere
- Prerendered a section in HuffYUV and put it back in the timeline
- Exported whole amv to HuffYUV
- Compressed the final encode in virtualdub using Full Recompress mode

that would all be "lossless" except for the last compression wouldn't it? No - it is VERY lossy. Look at this example:

http://www.absolutedestiny.org/yuy2rgbconversion.jpg

The first image here is the source, the second is the final image and the bottom image is the difference between the two.

You'll notice that in the 2nd image you can see that

a) Both top and bottom subtitles have faded
b) The background has become more like grey
c) The kanji now has a dark red shadow at the edges

and so on. The third image shows all the colour that has been lost and it is quite substantial really considering that you are hoping for it to be lossy. This is not an uncommon editing procedure for some people either but remember that just because you are using HuffYUV doesnt mean that everything is lossless as it will do a colourspace conversion every time it is given data as rgb.

Virtualdub Full Processing and Premiere work in RGB so everytime you use those you convert the colours. Also vfapi plugin uses RGB as well.

So, if you are using an RGB process - use HuffYUV's RGB mode wherever possible... it might be bigger but it will look better in the long run.
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Postby RadicalEd0 » Thu Oct 03, 2002 6:31 pm

eliminate vfapi and full processing because they are unnecessary for any amv I've ever done and you've got 1 conversion from yuv to rgb and back. Converting that picture 1 time can't possibly do extremely noticable visual damage and plus the effects of colorspace conversions are much more obvious on pure red text against a set color background than on actual video material (even if it is drawn anime). Not that the loss isn't a bad thing.. its just that its kind of too minute (normally) to get excited about.
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Postby AbsoluteDestiny » Thu Oct 03, 2002 6:58 pm

RadicalEd0 wrote:eliminate vfapi and full processing because they are unnecessary for any amv I've ever done and you've got 1 conversion from yuv to rgb and back.


Um... I'm aware of this.

However, many people will use the method shown above. I just made the example to point out that you can't put too much faith in the fact that you aren't losing "much" information. Many users do not realise that Full Compression mode will convert things to RGB before writing the avi file... and equally many users wont appreciate the difference anyway ^_^

I try and do as few colourspace conversions as possible - usually you will only need to do 2 (one from YUY into RGB duringediting and another from RGB to YUY for a divx distro) or 3 if you encode an mpeg with tmpg.

it was just an example :)
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Postby RadicalEd0 » Thu Oct 03, 2002 7:07 pm

'ts all good 8)
you also don't have to go 3 conversions when encoding to mpeg if you output in YUV and encode through avisynth (unless tmpg for some reason has to switch it to RGB before encoding, which would be a waste :? )
thats afaik
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Postby AbsoluteDestiny » Thu Oct 03, 2002 7:23 pm

RadicalEd0 wrote:(unless tmpg for some reason has to switch it to RGB before encoding, which would be a waste :? )


You're right - it would be a waste... and that's exactly what it does ^_^;;;
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Postby The Wired Knight » Thu Oct 03, 2002 7:23 pm

WTF???!!! I just rendered my AMV to see how it was going at 720x480 and it's at perfect quality but the file size is only 82 megs. I'm encoding in Mpeg 2 with NTSC quality and wav sound compression. What the hell is going on? Why is the file size so low?
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Postby Zarxrax » Thu Oct 03, 2002 7:26 pm

Wow, thats really interesting. I had no idea that multiple colorspace conversions could degrade the image like that. But I'm with RadicalEd, I really wouldn't need to do more than one colorspace conversion. Anyways, could you explain why that happens? The way I always sort of understood it was that in yuy2 mode, it used 1 quarter resolution for the chominace data, so basically you were geting 1 out of ever block of 4 chrominance pixels. Thus, all 4 of the pixels chominance in that block would be the same. Now if you converted that to rgb, since all 4 are the same, it would simply still copy them all the same, exactly like the yuy2 vid looked. Now if you were to convert that back to yuy2, it chooses the one pixel again, and converts the other 3 so they are the same... but since they are already the same then nothing would happen. Is my idea of this flawed? (Well I guess it must be, so rather, where is it flawed?)
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Postby RadicalEd0 » Thu Oct 03, 2002 7:28 pm

:| ......
how long is the video? because if its 4 minutes and you're using uncompressed wav that means you've got exactly 1388 kbps video bitrate using mpeg-2 at 720 x 480 resolution. Which should look a little bit like utter crap. er.. what resolution wav and how long is the video? :?
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Postby RadicalEd0 » Thu Oct 03, 2002 7:36 pm

@zarxrax
well it works out like this.. chrominace is stored at 1/2 the res of luminace. When the conversion to rgb occurs, all the chrominace/luminace data is essentially lost, and when it is re-compressed, it re-samples it at 1/2, which would theoretically look like 1/4th compared to the original. Thus, essentially, the loss and bleeding gets exponentially worse every time you convert from rgb back to yuv. Thats a rough explanation to say the least.
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Postby The Wired Knight » Thu Oct 03, 2002 7:39 pm

48 kHz wav file. And the video is 3:36 in length. and the quality is pretty damn good, I can send it to you if you want but I just don't get it. The quality is amazing and the file size is pretty much nill.
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Postby RadicalEd0 » Thu Oct 03, 2002 7:45 pm

48 khz 2 channel uncompressed wav
3:36
your video bitrate should be exactly 1574 kbps
thats 4.66 bpp
uh...
erm...
there must not be a lot of action in the video :shock:
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Postby The Wired Knight » Thu Oct 03, 2002 8:40 pm

Well granted there are a number of still shots but they only last for maybe five frames a piece. Included with teh wav of the audio track I've also got some of the series original audio in there. The video is pretty fast moving and hass 200+ scenes used in it. I can't figure out what in blazes is going on with this file size. I can send it to you if you want and you can tell me. Either way, whatever is going on, I'm not complaining.
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Postby Hitori » Thu Oct 03, 2002 9:36 pm

The Wired Knight - What kind of codec are you using?



I use the vob files in premiere now. Also edited in and exported with HuffYUV in YUY2 at 720x480.
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Postby RadicalEd0 » Thu Oct 03, 2002 9:44 pm

hes using mpeg-2
I'll gladly download it if you can host it somewhere or wait I'll IM you and see if we can connect n you could send it to me
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Postby RadicalEd0 » Thu Oct 03, 2002 9:47 pm

just kidding your not on aim.. uh, well try to IM me it when you read this
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