Hi Guys - A silly question, as there are no stupid ones ;)

If you look at torrents for 1080p movies, all (or most) have sizes around 8-9 GB and boast a resolution of 1080p, however i read in most of the threads here that average BD movies (without additional material) are around 20-25 (even 28) GBs... what am i missing?

If i download a 8 GB 1080p movie, am i not getting the BD resolution?

Hi Guys - A silly question, as there are no stupid ones ;)

If you look at torrents for 1080p movies, all (or most) have sizes around 8-9 GB and boast a resolution of 1080p, however i read in most of the threads here that average BD movies (without additional material) are around 20-25 (even 28) GBs... what am i missing?

If i download a 8 GB 1080p movie, am i not getting the BD resolution?

If we just look into the scientific part of your post.

You can compress a movie that contains 1080P information. The problem with compression is that you get block artifacts. That destroys detail. Sure in many cases the detail will be preserved. But the chance that the image is riddled with artifacts are bigger.

But storage on its own isnt the only factor that determine the quality of the encode. Two encodes on the same movie with the same storage size, can look very different depending on how the encode was done.

(We can write a entire collection of books on this subject)

Just like a DVD movie that takes 8GB, you can recompress the same movie to 4GB. Sometimes it wille and work, sometimes it will not.

Its not a linear relationship between bitrate and quality.

MovieSwede - Thanks for the quick reply, but i still dont have the spot on answer to my query.

I am very used to seeing all BDRips at 8.4 GB or so and ignoring the technicalities for a second, are you telling me that none of those 9 GB files are actual Blue Ray 1:1 captures but encoded in a compressed form (and hence definitely losing SOME of their PQ? or are they 99-100% same quality of PQ and SQ when played back via PS3 on a 1080p display?

MovieSwede - Thanks for the quick reply, but i still dont have the spot on answer to my query.

I am very used to seeing all BDRips at 8.4 GB or so and ignoring the technicalities for a second, are you telling me that none of those 9 GB files are actual Blue Ray 1:1 captures but encoded in a compressed form (and hence definitely losing SOME of their PQ? or are they 99-100% same quality of PQ and SQ when played back via PS3 on a 1080p display?

The only way of fitting a movie that is 20GB in size on a DVD9 is to recompress.

As for quality, its a factor of many things.

Encoding software, skills of the encoder, the movie itself etc etc.


To make a simple explination of a complex thing, what its hard on the encoder is changes in the picture. Since the encoder uses a series of frames to reach encoding efficiency. So a static shoot is much easier to encode then a shoot with lots of movment.

Also add the inclusion of random grain, that makes every frame look like its unique.

So its really on movie to movie basis, how much you can compress. Some can very well preserve a visual quality of 100% while other may go down 66%

So in general terms, you lose quality.

Got it, but how do you explain all 1080p Rips being exactly the same size (i.e. 8.5 GB) vs. the acutal BDs ranging from 25 to 35 Gb? And if everyone on the planet is encoding it the same way, a 3 / 4 times decrease in size should definitely (not maybe) mean a significant loss of quality. That means that all 1080p torrents on the web are nowhere near the actual bluray quality if you play a BD disk (considering all factors like display equal).

Got it, but how do you explain all 1080p Rips being exactly the same size (i.e. 8.5 GB) vs. the acutal BDs ranging from 25 to 35 Gb? And if everyone on the planet is encoding it the same way, a 3 / 4 times decrease in size should definitely (not maybe) mean a significant loss of quality. That means that all 1080p torrents on the web are nowhere near the actual bluray quality if you play a BD disk (considering all factors like display equal).

My guess is most will not be the same quality as BD. And the larger the display is, the more will the 8,5 GB rip show its flaws.

Can some be close to the quality, yes.
Will they be as good as the BD, no.

As or everyone encodes at 8,5GB, thats because its the hardlimit for placing any data on a DVD9.

That means that all 1080p torrents on the web are nowhere near the actual bluray quality if you play a BD disk (considering all factors like display equal).
What do you expect for free(theft) downloads of studio releases. :)

The best analogy is in front of you. If you have a jpeg picture from a camera, you may have various settings such as normal, fine, ultra fine etc. If you take the same picture to your PC and manipulate it with photoshop, you can save it in various quality settings which will take up different sizes on disk.

Generally, the highest quality settings can take up a lot more bits because there are much more fine detail preserved, but the lower quality settings are much more efficient as they take up much less bits to store.

As for the math, it's complicated. The compression works on macroblocks (typically 16x16 ) uses transforms into the frequency domain a block at a time (typically 8x8), and after that, each element in the block is divided by a (modifiable) predetermined number from a fixed sequence. This step is known as quantization. During compression, each number is divided by a quantization number for that position, during decompression, the number is multiplied back in. What is lost is the remainder of that division.

The bigger the quantization number, the smaller the compressed file becomes, but the more of the remainder is lost.

That is what separates a 8Mbps encode from a 30Mbps encode : different quantization.

There's actually other things that can come into play as how to make the best compression engines is a deeply guarded secret, it's not juist brute force and compression engines from different providers can behave differently, but my example generally applies to the different settings in the same compression engine.

The best analogy is in front of you. If you have a jpeg picture from a camera, you may have various settings such as normal, fine, ultra fine etc. .....

... So in other words, if I stand 1 feet away from a 50 inch 1080p tv and play a 1080p rip of 9GB and a actual BD of the same movie, i should definitely feel a significant difference due to loss of detail by slashing its size by 1/3rd, right?

And also in other words, a 1080p 9GB rip would not be (by any means) the right mode of display of superiority of 1080p capability?

I would expect to see differences for sure.

I can tell differences on most people's SD-DVD backup copies as well. A few people seem better at making their copies than others. Most don't seem to know how to get an exact identical copy.

... So in other words, if I stand 1 feet away from a 50 inch 1080p tv and play a 1080p rip of 9GB and a actual BD of the same movie, i should definitely feel a significant difference due to loss of detail by slashing its size by 1/3rd, right?

And also in other words, a 1080p 9GB rip would not be (by any means) the right mode of display of superiority of 1080p capability?
It won't be a huge difference for shorter films, because AVC is pretty good at hiding artifacts until you get into really low bitrates, but you'll lose some fine texture and it won't look quite as "clean". For long movies it'll look considerably worse.

Some thing else to keep in mind is that some shmoe sitting at home recompressing a movie on their computer is never going to get as good of a result as a trained professional sitting in a video editing suite with calibrated displayes and big buck tools to work with. Especially when their starting point is the studio guys work and not the master.

I have a number of friends that try to tell me that their torrents are the same as a BD disk but no one has shown me one that was even close, unless you are watching it on a puny screen. In which case you are probably better off with the DVD.

It doesn't take many artifacts or missing scenes to yank me right out of a movie. Just say no to torrents.

Hi Guys - A silly question, as there are no stupid ones ;)

If you look at torrents for 1080p movies, all (or most) have sizes around 8-9 GB and boast a resolution of 1080p, however i read in most of the threads here that average BD movies (without additional material) are around 20-25 (even 28) GBs... what am i missing?

If i download a 8 GB 1080p movie, am i not getting the BD resolution?

If there is little movement on the screen, then the resolution will be the exact same as BD. If there is rapid movement, then the compress and low bit rate will not keep up...BUT if you have a not so great LCD or plasma monitor, then it won't matter because they suffer from motion blur. Even with BD they can not display anywhere near 1080p during movement.

Where you WILL lose out is audio. Most torrents are only DTS or DD. Most BDs have some sort of lossless or uncompressed audio.

So my bet is if you have an average LCD 1080p monitor (any size) and only use the TV speakers, then most people would not tell the difference. If you have a DLP monitor and a nice receiver that supports newer audio codecs or 5.1/7.1 analog inputs, then you will be able to tell more easily.

If there is little movement on the screen, then the resolution will be the exact same as BD. If there is rapid movement, then the compress and low bit rate will not keep up...BUT if you have a not so great LCD or plasma monitor, then it won't matter because they suffer from motion blur. Even with BD they can not display anywhere near 1080p during movement.

This is true after some elapsed time after the scene change in the slow portion of the clip. At the point of the scene change, for a couple of frames, a low bitrate encode still can show artifacts if the first static frame is complex enough, but this artifact disappears a few frames later if the clip is really friendly.

This is true after some elapsed time after the scene change in the slow portion of the clip. At the point of the scene change, for a couple of frames, a low bitrate encode still can show artifacts if the first static frame is complex enough, but this artifact disappears a few frames later if the clip is really friendly.

Good point.

One effect many forget to mention is that encode is also an effect of processing.

You can compress more with the same visual quality, but you will lose encoding speed as a sideeffect.

If there is little movement on the screen, then the resolution will be the exact same as BD. If there is rapid movement, then the compress and low bit rate will not keep up...BUT if you have a not so great LCD or plasma monitor, then it won't matter because they suffer from motion blur. Even with BD they can not display anywhere near 1080p during movement.

Where you WILL lose out is audio. Most torrents are only DTS or DD. Most BDs have some sort of lossless or uncompressed audio.

So my bet is if you have an average LCD 1080p monitor (any size) and only use the TV speakers, then most people would not tell the difference. If you have a DLP monitor and a nice receiver that supports newer audio codecs or 5.1/7.1 analog inputs, then you will be able to tell more easily.


Everdog... i have a Samsung LN46a550, do you consider that a lousy LCD or one that can manage motion blur well? Secondly, if audio is the bigger loss, how can i tell which audio am i getting from a m2ts file? any program to tell me all the info of my files? like which bitrate, which framerate, what kind of audio it's producing etc?

Thanks.

The quality of the torrent BDrips will depend greatly on the person who re-encoded it. I've seen some truly awful BDrips with macroblocks everywhere, and I've seen some truly beautiful BDrips where I just don't feel the need to import the actual title for $80. (Anime on Blu-ray in Japan, say hello! And DIAF!)

Will the quality match the original 20GB+ encode? No, it won't, but x264 in the hands of a skilled amateur is nothing to sneeze at, and keep in mind that a lot of that 20GB+ is occupied by the lossless soundtrack which BDrips omit. You're still talking about a 50% or more reduction in filesize and bitrate, so it will absolutely not be transparent to the original encode on the disc, but between sacrificing a little quality and getting reamed for no good reason to the tune of $80 to import anime, I'll go with the sacrificing a little quality.

There are non-recompressed HD DVD and BDrips floating around too. If you don't mind downloading 20GB+ they are exact reproductions of what was on the disc, usually with one lossless soundtrack intact and remuxed to .mkv (Matroska) container format is what I often run into. I've never had the patience or bandwidth to download 20GB+ and wait 1-2 week nor do I have the hard drive space, but they are out there.

Everdog... i have a Samsung LN46a550, do you consider that a lousy LCD or one that can manage motion blur well? Secondly, if audio is the bigger loss, how can i tell which audio am i getting from a m2ts file? any program to tell me all the info of my files? like which bitrate, which framerate, what kind of audio it's producing etc?

Thanks.

It looks like your Samsung has 310 lines of vertical resolution during motion...
http://hdguru.com/wp-content/uploads/2008/09/2008-resolution-tests-125-hdtvs.pdf

It looks like your Samsung has 310 lines of vertical resolution during motion...
http://hdguru.com/wp-content/uploads/2008/09/2008-resolution-tests-125-hdtvs.pdf

That chart is another way to show why a plasma easily beats an LCD in moving video. Which goes to my main point again that the main HT must be plasma (while the 2nd/3rd TV for consoles should be LCDs).

That chart is another way to show why a plasma easily beats an LCD in moving video. Which goes to my main point again that the main HT must be plasma (while the 2nd/3rd TV for consoles should be LCDs).

I take a LCD projector over plasma any day.

Even if plasma can deliver a better PQ, is still just a TV.

That chart is another way to show why a plasma easily beats an LCD in moving video. Which goes to my main point again that the main HT must be plasma (while the 2nd/3rd TV for consoles should be LCDs).

Ya sure... Show me a Plasma based projector so I can project my movie at 106" for $4k (including the electric screen) like I can do with my LCD projector and we'll talk.

I prefer a really BIG screen in my HT and believe me I don't suffer for lack of resolution. HT enjoyment is not equal to some number on a spreadsheet.

Think of the movie scenes you enjoy most in HD. Are they fast action sequences, or slow pans and still shots?

I personally enoy the highly details still shots and slow pans that let me take in all the detail. While I do have a plasma TV, my HT room has an LCD projector (I would prefer a high-end DLP one though).