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Is there any way to detect how much compression has been applied to a DVD??
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tafkas
Junior Member
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25. September 2007 @ 20:45 |
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A friend recently sent me some burned DVDs which came from sources that should have required no compression to fit on single layer DVDs, yet what he sent me look TERRIBLE. Some are are heavily pixelated, like a photograph that has been turned into a low resolution JPG.
Is there a way to find out how much (if any) compression was applied to a burned DVD copy from looking at it with some kind of software on the PC? Or at least get an idea of expected "quality" based on some kind of "bit rate" information or something like that?????
Also I am curious how to go about understanding what might have gone wrong on his end - for example are there known issues with certain programs like nero (or something???) that are going to compress rips or degrade the quality in some way by default that I need to tell him about?
Thanks for any tips.
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aabbccdd
Suspended permanently
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26. September 2007 @ 00:07 |
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once its on a DVD-5 you can't tell how much it was compressed.
is he backing up store bought DVDs? or are they from other sources? downloaded etc.
using low grade media (memorex etc.) and burning to fast can cause the problems you mentioned.
tell him to use Taiyo Yuden or Verbatim burning NO faster then 8x max for the best quality
This message has been edited since posting. Last time this message was edited on 26. September 2007 @ 00:08
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JoeRyan
Senior Member
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26. September 2007 @ 07:14 |
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The description of the picture quality has nothing to do with the quality of the medium used. Flaws on a disc can cause pixel blocking (the green blocks that show up when error correction circuitry is overwhelmed), but the description tafkas seems to be describing in terms of resolution sounds more like the result of heavy compression. The amount of compression can be determined by a program that expresses the data flow in megabits/second from a drive playing a DVD at 1X speed. However, multiple passes through different encoders/decoders can also have an effect on picture quality even at high bit rates; and that might be a factor.
The reference to Memorex as "low grade" not only has nothing to do with the user's problem, it is erroneous unless one accepts the wacky ratings of digitalfaq as factual and scientific and not the source of laughter that optical engineers consider it.
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res2cue
Suspended due to non-functional email address
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26. September 2007 @ 07:15 |
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paper labels can also cause those problems, but it's usually accompanied by frames freezing. My best guess would be heavy compression. What movie? Do you have all menus, bonus features and previews?
Hiram 319
AF & AM This message has been edited since posting. Last time this message was edited on 26. September 2007 @ 07:16
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JoeRyan
Senior Member
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26. September 2007 @ 08:47 |
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Paper labels cause the same kinds of problems that physical defects cause, and those problems show up in the last third of a disc's full capacity. The labels pull the edges of the disc up in a "cupping" effect so that the laser can no longer accurately focus or track. The change is imperceptible to the eye, but it is enough to cause pixel blocking and finally the locking up of the playback.
The symptoms tafkas is describing seem to arise from the very beginning of the disc and last throughout the program. This sounds like blowing up a downloaded video onto a large screen and seeing all the compression artifacts: blocks of color/detail instead of fine resolution and sharp contrasts. That is symptomatic of heavy compression or even of multiple codecs on a program. Expanding an MP3 audio file to a .wave file, for example, doesn't fill in the missing information; and converting an ACC file to WMA to MP3 and then to .wave introduces a great many distortions that .wave cannot repair. The more I think about this case, it sounds as though the original files were heavily compressed video downloads converted to MPEG-2 to play on DVDs. (Putting lipstick on a pig doesn't make her a better date.)
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Moderator
1 product review
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26. September 2007 @ 09:39 |
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Quote:
(Putting lipstick on a pig doesn't make her a better date.)
That would depend on how many beers you've had...;-)
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AfterDawn Addict
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26. September 2007 @ 10:41 |
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Quote:
Some are are heavily pixelated, like a photograph that has been turned into a low resolution JPG.
I have lots of those.They are on my 'Ritek' collection - the same backups, using the same settings on the same software, but burned on Verbatim and Maxell are A1.
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res2cue
Suspended due to non-functional email address
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26. September 2007 @ 11:32 |
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Originally posted by JoeRyan:
Paper labels cause the same kinds of problems that physical defects cause, and those problems show up in the last third of a disc's full capacity.
wrong on that one, paper label will and do cause problems from the very start of playback. I have personally proved this theory more than once.
Hiram 319
AF & AM
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JaguarGod
Senior Member
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26. September 2007 @ 13:36 |
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Uncompressed DVD (I think it's called D1) is about 200mbps to 250mbps (keep in mind the best you will ever see on HD DVD or Blu-Ray is 25mbps, roughly 1/10 the bitrate of max D1, but I think they use D5 on HD).
A DVD Video Disc can handle a max of 9800kbps (kilo not mega). you must remove from it audio, muxing overhead, and such, so let's say 9300kbps would be a full quality DVD Video.
Here's how to figure out how much compression is on the disc:
size = [(vbr + abr) / 8] * t in seconds
Say that the size of the movie (not the whole disc, just the main movie) is 3500MB and it has two DD 5.1 audio streams. Also, the movie is 93 minutes 27 seconds.
3584000 = [(vbr + 896) / 8] * 5607
639.18 = (vbr + 896) / 8
5113 = vbr + 896
4216 = vbr
The bitrate will not be exact, but within 100kbps
Now, to figure out compression:
actual bitrate/max bitrate
&
actual bitrate/uncompressed bitrate
4216/9300 = 45.3% or 2.21:1 quality based compression
4216000/200000000 = 2.108% or 47:1 overall compression
4216000/250000000 = 1.687% or 59:1 overall compression
Use quality based compression to see how much the DVD was compressed compared to the maximum a DVD VIdeo Disc can handle and Overall to see how much compression was actually put on the original video.
So in this case, the movie would have been 45.3% of max quality meaning it was compressed 2.21:1 of the max a DVD Video can handle. Also a 54.7% quality loss.
In overall compression, this movie was compressed somewhere in between 47:1 & 59:1 (the 59:1 is probably more accurate). Yes, they are typically compressed that much. They have used the same bitrates since DVD came out even though before they used Single Layer DVDs and now they are Dual Layer.
Oh, and movies that come out of $ony Studios are generally lower bitrate than the example I gave. Possibly to show the difference between Blu-Ray and DVD & promote Blu-Ray more, so they give you crippled DVDs...
This message has been edited since posting. Last time this message was edited on 26. September 2007 @ 13:45
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res2cue
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26. September 2007 @ 13:45 |
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there is no way in the world I could ever dispute that...
Hiram 319
AF & AM
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JaguarGod
Senior Member
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26. September 2007 @ 13:47 |
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LOL!! Yeah, I went a little crazy there.
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AfterDawn Addict
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26. September 2007 @ 14:55 |
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Quote:
3584000 = [(vbr + 896) / 8] * 5607
@JaguarGod
Hats off to you, but what are the 896 and /8 numbers?
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JaguarGod
Senior Member
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26. September 2007 @ 16:48 |
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Quote:
Quote:3584000 = [(vbr + 896) / 8] * 5607
@JaguarGod
Hats off to you, but what are the 896 and /8 numbers?/Quote:
The 896 came from the assumption of 2 Dolby Digital 5.1 tracks. What I did, was multiply 448 by 2 since each 5.1 track is almost always 448kbps. This will change with every DVD, because some will have 192kbps stereo tracks, DTS tracks which are going to range from 768kbps to 1536kbps (the latter is on earlier DTS releases), and very rarely 1536kbps uncompressed stereo tracks.
The 8 is to convert bits to bytes. You are dividing the bitrate which is in kilobits per second by 8 to get kilobytes per second.
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tafkas
Junior Member
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26. September 2007 @ 19:32 |
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Thanks for all the comments!
Yes, I was referring to something that looks pixelated all the way through, nothing to do with bad media or flaws caused by labels or anything like that - just compressed when copied and quality degraded, like taking an audio WAVEFILE and converting it to MP3 but using very low bitrate & losing quality.
Jaguar posted some very interesting info. But it sounds like there is no simple tool/program for me to use that can look at the data on the disc and say "aha! you were degraded/compressed" though.
Thanks guys :)
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