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Hanks183
Jan 22, 2008, 11:10 AM
Hello all!

I've been reading this forum for a while now but this is my first post!

I just got an :apple:TV and I'm now wanting to get digital copies of all my DVDs. I am wondering about quality settings in general (like bitrate, etc.) in Handbrake or any software. I would like to get an exact copy (i.e. 480p video quality) into iTunes, and could care less about the size of the file.

I know that the bitrate you choose has some sort of ceiling (like a bitrate of, say, 6000 will not provide better results than, say, 12000), but how do you find that limit other than trial and error?

480p at 19:9 ratio is 720x480 pixels, but how does bitrate come into play?? I have done a bunch of searches online but I cant find any math to back up peoples claims that one bitrate is better than another!!

Thanks in advance!



mindcrash
Jan 22, 2008, 11:19 AM
Well, I think what you have to be aware of is the fact that :apple:TV has a 4GB file limit.

Personally, I'm using the :apple:TV preset in Handbrake, adding 2 pass encoding with a turbo 1st pass, and I'm VERY pleased with the results on a 32" LG LCD through the HDMI input. The bitrate for that preset is 2500.

spice weasel
Jan 22, 2008, 11:40 AM
I also use the Apple TV preset on Handbrake. Only I only use 2-pass on some movies, simply because it takes too long to encode on my G5 iMac. Honestly, I notice very little if any difference on my 37" Toshiba LCD.

MikieMikie
Jan 22, 2008, 12:14 PM
Hello all!


Back at ya! Welcome.

I've been reading this forum for a while now but this is my first post!

I just got an :apple:TV and I'm now wanting to get digital copies of all my DVDs. I am wondering about quality settings in general (like bitrate, etc.) in Handbrake or any software. I would like to get an exact copy (i.e. 480p video quality) into iTunes, and could care less about the size of the file.


I have the same attitude. I find that for almost-all encodes, the Apple TV preset in Handbrake is DVD quality. I have a 57" HDTV, so I would notice bad/inferior encoding.

On rare occassion, I have seen in some scenes, on some encodes, a blockiness/mosaic effect in clouds, or smoke, so I will re-encode them. This is rare when using AppleTV preset in Handbrake, more common in Visual Hub.

Size of the file shouldn't be an issue -- most end up between 1.5 and 2 GB.


I know that the bitrate you choose has some sort of ceiling (like a bitrate of, say, 6000 will not provide better results than, say, 12000), but how do you find that limit other than trial and error?


The difference between 2500 and most rates below it are noticeable. The next big bump happens at 5000, I believe, but the visual difference is minimal for the most part. The best thing to do it play with it and see for yourself. The AppleTV presets are really the best settings for most people on average.

480p at 19:9 ratio is 720x480 pixels, but how does bitrate come into play?? I have done a bunch of searches online but I cant find any math to back up peoples claims that one bitrate is better than another!!

Thanks in advance!

Bitrate is the speed at which an update can happen. If you're updating the screen (for a movie) at 24 fps, then a higher bitrate is a waste of space. If, on the other hand, the scene is complex, like an explosion, and it changes significantly from frame to frame, then you would want the update (the new frame) to appear as quickly as possible (i.e.: at i/24th of a second). The more data you push down the pipe, the more likely it is that you'll miss this frame update.

Hope this helps.

Avatar74
Jan 22, 2008, 12:35 PM
480p at 19:9 ratio is 720x480 pixels, but how does bitrate come into play?? I have done a bunch of searches online but I cant find any math to back up peoples claims that one bitrate is better than another!!

Thanks in advance!

I assume you mean 16:9 (above) but anyway...

The math is very complicated at this stage because we're talking about compression algorithms that don't just apply straightforward math the way that, say, Linear PCM audio (an uncompressed format) does.

But generally speaking, the bitstream size for video is dictated by certain factors, which include chrominance (color value per pixel), luminance (brightness value per pixel), motion (the degree and frequency at which the value of each pixel changes), and the like.

There's a point of diminishing marginal returns where the larger the bitstream, the more processing power is required to handle it for no perceptible benefit in clarity, color and contrast. In the MPEG-4 world, this varies depending on the profile type and version being used.

Main Profile is designed for larger bandwidth applications like broadcast. Baseline profile is used for media streaming. High Profile is used for extremely large bandwidth applications like uncompressed digital cinema. At each of these profile levels there are different algorithm optimization schemes to get the best performance for the task.

What we're finding with AppleTV is that the OPTIMUM bandwidth for a DV NTSC encode (720x480 frame aspect with 0.9 pixel aspect) is around 2300 to 2500 kbps. Lower than that, and artifaction becomes noticeable. Higher than that produces no real discernible benefit.

The straightforward calculation in an uncompressed video stream would be something like this:

bits per channel x # of channels (e.g. RGB, YPbPr) x # of pixels per frame x frames per second = per second bitstream rate

So, a 2540p bitstream uncompressed would be about 275 Mbps... this is the next gen UHDV format being pushed with the RED camera for digital cinematography.

But this kind of math doesn't work even when talking about plain old DVD's because even MPEG-2 is a lossy compression format. We'd have to know the entire formula to be able to give you a mathematical breakdown of how we arrive at the figures for data consumption even with MPEG-2, nevermind MPEG-4 which is even more complex.

I wish I could produce the math for you on this the way I can break down audio but the fact is, I don't know all the math behind the MPEG-4 AVC algorithm... and even if I did, it's not like it's basic algebra. The mathematical explanation for that particular codec may very well likely not make any sense to you anyway. I'm not even sure I'd understand it.

jersey10
Jan 22, 2008, 01:08 PM
A related question - I have been using Handbrake to convert a bunch of episodes of Seinfeld I have on DVD. I have been using the Apple TV presets, with one exception. I have been checking "keep aspect ratio" instead of the "anamorphic" setting. I have done this because the anamorphic setting seems to squish the picture together too much when I preview it in Handbrake. The "keep aspect ratio" setting seems to look more natural.

Is this the best way to do this for a DVD of a television show such as this that is not a widescreen movie?

And should I use the anamorphic setting instead of the "keep aspect ratio" if and when I convert a widescreen DVD movie?

Any help would be appreciated. Thanks.

MikieMikie
Jan 22, 2008, 03:38 PM
A related question - I have been using Handbrake to convert a bunch of episodes of Seinfeld I have on DVD. I have been using the Apple TV presets, with one exception. I have been checking "keep aspect ratio" instead of the "anamorphic" setting. I have done this because the anamorphic setting seems to squish the picture together too much when I preview it in Handbrake. The "keep aspect ratio" setting seems to look more natural.

Is this the best way to do this for a DVD of a television show such as this that is not a widescreen movie?

And should I use the anamorphic setting instead of the "keep aspect ratio" if and when I convert a widescreen DVD movie?

Any help would be appreciated. Thanks.

I encode all widescreen films with Handbrake, set to anamorphic "on."

It makes a difference.

jersey10
Jan 22, 2008, 04:07 PM
How do you handle stuff that is not widescreen, such as TV shows?

zedsdead
Jan 22, 2008, 04:39 PM
Do you plan to have these files play on any other Apple Devices (iPod/iPhone) or just the Apple TV? That's makes a difference as to what settings to employ.

jersey10
Jan 22, 2008, 05:05 PM
Just on my High Def plasma via Apple TV.

Hanks183
Jan 22, 2008, 05:16 PM
I assume you mean 16:9 (above) but anyway...

Yea I did mean 16:9, I was typing a liiiiittttlle too fast :D

Nice response though, I figured the math behind video would be really really really hard to understand and thats why its imposible to find on the internet.

Do you have any idea how close a DVD encoded at an average of 2500 kbps would compare to a 480p DVD? I know it looks close, maybe slightly darker for whatever reason, but do you how close it is using even fuzzy math??



Do you plan to have these files play on any other Apple Devices (iPod/iPhone) or just the Apple TV? That's makes a difference as to what settings to employ.

I am pretty much just going to watch my movies on the :apple:TV - if I want to watch them on something else I'll just re-encode them to that other format.