Digital Video Quality

[jason69uk]

Ive asked things like Can AVI's eventually wear out and fade like videos can which the anbswer is no.

But thinking about it what i really mean is say if i have a rip on a film that's 1:10 mins long and a 700 MB rip and its divx so the quality would be quite good.. But if i kept watching it and watching it would it eventually end up the quality of a 650MB film thats 2 hoursl ong if u know what i mean. Cos a 650 MB film thats 2 hours long would be bad quality wouldn't it. But after time say i have a film on the computer for 4 years. Thats a really clear rip and a good picture after being on there for 4 years will it end up the quality of a film thats 2 hours long ripped at say 650MB. Or definatly not? would it go blocky in places if i had bad sectors and bad fragments i mean noticeably blocky like so much so i cant see the picture properly??

[mats.hogberg]

Still no. Sure, solar flares, cosmic radiation, a nearby nuclear power plant going up in smoke and such, could (more or less hypotetically) damage the media your AVI is recorded to (CD/DVD/HDD/Flash RAM/...) but as long as the hardware is intact and functioning as before, so will what you put on it be.

/Mats

[lechtin]

Digital video, like any digital data, is only a series of 1's and 0's. Once stored, reading it any number of times will not degrade it. Any degradation would imply some 0's and 1's losing or switching their state.

It's like asking if a word document will be readable after it's been on your hard disk for 4 years. The answer is yes unless there is data corruption, but then it's likely going to need some data recovery tool to get back.

[jason69uk]

"Still no. Sure, solar flares, cosmic radiation, a nearby nuclear power plant going up in smoke and such, could (more or less hypotetically) damage the media your AVI is recorded to (CD/DVD/HDD/Flash RAM/...) but as long as the hardware is intact and functioning as before, so will what you put on it be.

/Mats"
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That's way beyond me Mats could u explain it for a thick person please.

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'Digital video, like any digital data, is only a series of 1's and 0's. Once stored, reading it any number of times will not degrade it. Any degradation would imply some 0's and 1's losing or switching their state.

It's like asking if a word document will be readable after it's been on your hard disk for 4 years. The answer is yes unless there is data corruption, but then it's likely going to need some data recovery tool to get back."

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Thanks, so if i did have corrupted data then it would definatly be noticable whilst playing an AVI back because such issues would occur such as freezes and really blocky picture??

[mats.hogberg]

I think what lechtin and I are saying is the same - We're speaking digital data here, and even if digital data (bits, 0 and 1) can be altered, it can never "go bad". So, there's no aging or wear and tear of digital data. We can read it 1.000.000 times, or not at all, it will still be the same.
If we talk digital video, we might spot a bad data like a miscoloured pixel now and then, but we won't see something like an overall faded image, or something like that. Had it been a Word document, we'd notice that as an "e" being replaced by a "d" in a word. In this case, I'd suspect my HDD going bad, or I have left the CD-R in the sun. My action would then to backup the data to a new media or to another HDD, where it'd be safe until that media starts to fail.

/Mats

[junkmalle]

In some ways, digital data can be more vulnerable than analog. For example, what if your fourcc code in a DIVX video changed from DX50 to EX50 -- a single bit change. You would no longer be able to play the video at all! Fortunately, modern storage devices are extrememly reliable.

[jason69uk]

What could happen if it was EX-50??

[mats.hogberg]

The player wold try to find out what kind of codec is in use, and see EX-50, which it has no idea what it is, and hence refuse to play. (DX-50 is DivX 5.0, which the player would understand, and use the DivX codec to decode the movie.)

/Mats

[jason69uk]

Sorry, lol im talking about playback on a pc, not a standalone divx dvd player.

[junkmalle]

Sorry, lol im talking about playback on a pc, not a standalone divx dvd player.

Same thing. The player would not be able to determine what codec was used. It therefore could not uncompress the video to play it.

[mats.hogberg]

Sorry, lol im talking about playback on a pc

So was I, but the same principle applies regardless, as junkmalle says.

/Mats

[jason69uk]

but what would it look like if data was corrupted would the blockiness be noticeable and it wouldnt just look like a low quality bad rip with loads of pixels on it, it wld be properly pixelated so much so i wouldnt be able to see the picture and id defoinatly know if data was corrupted cos it would go VERY blocky, if its really pixelated anyway isit just a bad rip?

[junkmalle]

Most codecs result in pictures like this when small errors occur:



A single bit in an MPEG stream can cause errors like this. The error can last for as long as half a second.

[jason69uk]

and this can be caused from bad codecs yeah? and that annoying crystal player..

So thats what it would look like if i had a corrupt hard drive thats the type of pixelation i would get?

If it was just a bad rip it would be b;locky all the tome wouldnt it?

[mats.hogberg]

junkmalles screen shot is from a bad mpeg file. As there of course is a codec responsible for decoding the mpeg compressed data, different codecs might treat the errors differently, but that was not the point here, right?
This kind of errors could be caused by a corrupt HDD, yes.
You have to define "bad rip", but if we say it's a "reencoding of digital video using too low bit rate" it'd be blocky not all the time, but when things in the picture move, which is what things are prone to do in a movie (or else we wouldn't call it "movie"), so it'd be blocky most of the time.

/Mats

[junkmalle]

Here's a sample of a bad (too low bitrate) rip with XVID:



Note the 8x8 pixel blocks all over the place.

[jason69uk]

right ok guys, now.

The first picture you lot showed me of the lady in her 2 piece thing, lol that looked blocky.. Now thats the type of blockiness you could get a from a corrupt hard drive, or a badly burned CD??

The picture you showed me below can only be caused from a too low bitrate whilst encoding or reencoding, right??