Video quality vs. bitrate?

[W_Eagle]

My understanding, based on my experience, is that when authoring DVD (or SVCD/CVD for that matter), as for quality, the situation is like this:

Resolution, which means sharpness (horizontal resolution) isn't affected at all by the bitrate used;
Colors, hue, saturation, etc, aren't affected at all by the bitrate used;
The only problem with using low bitrate is having at times digital distortions, or "blockines".
Thus, the lowest bitrate that will not add digital distortion, like "blockines", is good enough to maintain full video quality.
Am I right here, or is there any other quality degradation when lowering bitrate?

[bugster]

You are pretty much on the mark, but higher bitrate can help increase 'sharpness', especially of minor background details too.

Also, if you use a lower resolution, you can often get away with a lower bitrate. As there are less pixels to encode, less data is needed to encode them. Sure 352*480 is never going to look as good as 720*480 can look, but you can achieve the max quality available at the lower resolution with a much lower bitrate than needed for the best quality at the higher resolution.

[dvdhelpr]

but how does the lower res affect the appearance on you tv?

like do u get it looking small screen on widescreen?

thanx

this would be uaseful for encoding those videos that tmpge wizard doesn't manage to fit on a dvd-r.

[bugster]

but how does the lower res affect the appearance on you tv?

like do u get it looking small screen on widescreen?

thanx

No, the way it is displayed on your TV is determined by the DAR flag (Display Aspect Ratio) and has nothing to do with resolution. Remember, both 16:9 and 4:3 mpegs, at full D1 resolution, are 720*480/576 (NTSC/PAL).

[dvdhelpr]

oh no. i mean thwe difference between 354* and what ever it is


and 756* or what ever it is.

thanks.

[bugster]

Yeah, thats what I meant too. It looks the same shape on your TV irrespective of the resolution. I was trying to explain that resolution and display aspect ratio are two different things. (obviously not very clearly)

[Shudder]

Do you have any mpeg movies? I'm going to doubt they fill your entire screen. In a media player run them at 200% zoom. Or run a divx or whatever that's lower than your tv's max resolution and run it fullscreen.

At a lower bitrate, lower resolutions will look less blocky, but a little more "fuzzy" since all the detail's not there. Same thing if you take an image and resize it to a bigger resolution. it can only do so much guesswork with such little detail, so it won't be as sharp.

It's all up to your preference really, I will take a lower resolution over blockiness anyday. When I did divx encodes if I had any blockiness I'd redo it with a lower resolution.. to me the blocks are way more annoying than the slight loss of sharpness

[vitualis]

Resolution, which means sharpness (horizontal resolution) isn't affected at all by the bitrate used;
Colors, hue, saturation, etc, aren't affected at all by the bitrate used;
The only problem with using low bitrate is having at times digital distortions, or "blockines".
Thus, the lowest bitrate that will not add digital distortion, like "blockines", is good enough to maintain full video quality.
Am I right here, or is there any other quality degradation when lowering bitrate?

That is actually quite incorrect.

If you mean resolution in terms of "sharpness" or "detail", then IT IS AFFECTED BY THE BITRATE. If you mean resolution in terms of the framesize, then no, it isn't affected.

Colour reproduction is also affected by the bitrate.

Basically, with MPEG encoding, as you drop the bitrate you will start to loose the amount of detail in the image, the accuracy of the colour reproduction and if you loose ENOUGH detail in a certain area, then the macroblocks in the image become apparent (i.e., blocking).

Depending on how the particular MPEG encoder works, exactly which is more obvious first may be different.

@ Shudder, I don't think you understand what bugster and the others are talking about.

For VCD, SVCD and DVD, regardless of the actual framesize involved, they fill the screen of the TV (assuming you are using a DAR of 4:3).

Thus, a full frame VCD with a framesize (framesize and resolution are DIFFERENT concepts) of 352x240 will fill the TV screen.

A full frame SVCD with a framesize of 352x480 will fill the TV screen.

A full frame DVD with a framesize of 720x480 will fill the TV screen.

The difference is the RESOLUTION. A DVD has over 4 times the number of pixels in each frame compared to a VCD. Thus, it has over 4 times the resolution. That means, on a TV (which at best can just about show the resolution of a DVD), a DVD can look much sharper (i.e., can show more detail) than a VCD.

Note: the operative word is can, not must. There are many reasons why in real life a DVD may not look hugely better than the equivalent VCD.

Regards.

[W_Eagle]

Thank you very much bugster and vitualis, both of you have been helpful.

[vhelp]

.
.
One other point, that was left out of W-Eagle's equation (or response thereof)
is the Bitrate Mode used for the encoding.

If you use TMPG's CQ mode, you'll deffinately get different filesizes, becaues
CQ is based on Quality, not size (though size is factored in to a small degree)

If you use TMPG's other mode, like CBR (and I think 2-pass) you may get
about the same filesize, though I'm not sure about the 2-pass, unless the
2-pass is abased on the same "Resolution" slope. For instance, if the algo
is basing on a predefined slope (inside the 2-pass VBR) then I would assume
that 352 vs 720 vs 480 etc would not matter as much, as the filesize will be
about the same. This can be evident by observing the "macro-blocks" or
"square pixelation" you see in high-action scenes. The higher the resolution,
the more pixelation on THAT given slope.
.
.
Now, I'm not saying that there is a BIG difference in MB's.. just saying that
there is a noticable size difference (under CQ mode, that is) And, if you do
encode a whole full length source, you'll then see the difference in final file
size (again, w/ CQ mode)

-vhelp

[lordsmurf]

I was under the impression that it was the discrete cosine that determined the quality of the color/hue/saturation/chroma, not the bitrate, at least not in MPEG1/2 format. And even then, DC8 is fine, though DC9 is better (used commercially on many DVDs), with DC10 being the max (being used by a lot of the DVD recorders).

At a proper bitrate, resolution is not effected by bitrate. Meaning the clarity will remain as long as minimums for said resolution are maintained adequately. That all sounds confusing, I know. Example: 352x480 can be equally sharp at 2.5 MB/s as it can be at 15.0 MB/s. They are independent until corruption occurs from lack of bitrate (which is not really an equation of bitrate=resolution, but rather resolution can be affected by an equation where the bitrate is inadequate). It's an affect, not an effect.

Storage pixels and playback aspect ratio are independent of one another. 7x480 and 720x480 will play back at the same "tv size" as long as the 4:3 flags are in place.

And then, let's not forget you cannot surpass your source. So saying that 352x480 looks "fuzzy" compared to 720x480 means zilch if your source is VHS or television.

[W_Eagle]

Thank you all. It looks like we have an almost full picture now.

[Gazorgan]

On my 27" TV I can tell the difference between 1/2 D1, SVCD and full D1. But then I do video all the time, I see crawling backgrounds all the time p

However, my wife, kids, and friends can't really tell the difference.

It's like this. Forrest and Trees. Some Forrests are thicker than others, but they are still forests. A few dead trees here and there are hardly noticeable when looking at the forrest.