resolution vs bitrate

[need4speed]

dumb question, so pls forgive if old.
Encoding divx in sight of viewing on plasma screen the best option is higher bitrate and lower resolution or higher resolution and lower bitrate??

[bond]

are you going for a 1/2 CD/DVD encode? if yes than you have a fix bitrate anyways

[need4speed]

are you going for a 1/2 CD/DVD encode? if yes than you have a fix bitrate anyways
well, not too sure. No real fixed parameter, just trying to underrstand if on a 43" screen a highter bitrate and lower res is better than lower bitrate and higher res.
Just curious, really.

[bond]

well simple answer: a big screen needs a high resolution and a high bitrate ;)

high res with low bitrate is bad, low res with high bitrate is a waste

[DigitAl56K]

Plasma screens are particularly good for showing up blocking artifacts. If I were encoding for display on Plasma I would either raise the bitrate greater than normal, or ensure that my decoding device supported deblock post-processing.

[MCSmarties]

Hello,
I would like to continue this thread because the title applies exactly to my question even if the application is a bit different.

I want to encode movies for a portable media player (4.3" screen, 16:9 ratio with resolution 480 x 272) and keep the file size relatively small (aiming at 500 MB for a 2h movie).

The primary purpose is to watch the movie on the player itself of course, yet since it has video out I want to encode in such a way that I still get "decent"
quality on an external TV (nothing fancy, just so that I could watch my movies on a hotel room TV for example without getting tears in my eyes!).

Keeping the small filesize requirement in mind, should I:
- aim for higher resolution and sacrifice bitrate, eg quality or
- fix the resolution at 480 x XXX and use the highest bitrate possible?

I know this is a case of "judge yourself what you like best" but is there a rule of what minimum resolution I should aim for to have a decent picture on a no-frills TV set?

[stephanV]

I dont see how resolution and bitrate are related in the way you are trying to suggest.You say you want a 2 hour file to be 500 MB, so that fixes the bit rate completely regardless of what resolution you choose.

I know this is a case of "judge yourself what you like best" but is there a rule of what minimum resolution I should aim for to have a decent picture on a no-frills TV set?
If you can define what "decent" means to you, maybe... :p

[MCSmarties]

stephanV, thanks for your input.
Now I wonder if I am wrong about something fundamental...

Assume you got a 2h movie and encode it (using whatever codec) to a file weighing 500 MB.
Won't the picture have to be compressed much more (hence lower bitrate) if you encode at say 720 x 480 than at 480 x 272?
The way I understand it, the codec has to put much more information into a frame that measures 720 x 480 pixels and hence
compress the movie much more - for a given file size - than for a frame measuring only 480 x 272 pixels?

What I really wonder about is whether a resolution of 480 x 272 is ok to view on a say 30 inch analog TV (even using the highest bitrate possible)
or if you NEED a higher resolution (regardless of bitrate) for scaling purposes?

Thanks for bearing with me, I'm sorry if I sound clueless!

[stephanV]

No, bit rate is proportional to file size --> [file size] = [file length] * [bit rate].

So if you choose, say, 500 kbps for a file with a res of 720x480 or 352x240, both will come out the exact same size as long they have the same lenght. You are right that the compression factor is higher because the codec can spend less bits per pixel on a higher resolution.

What I really wonder about is whether a resolution of 480 x 272 is ok to view on a say 30 inch analog TV (even using the highest bitrate possible)
or if you NEED a higher resolution (regardless of bitrate) for scaling purposes?
You really have to try that yourself. It can be ok but, as always, YMMV. To give you a comparison: VCD uses resolutions of 352x288 for PAL and 352x240 for NTSC. So if you think VCD looks ok, then you're safe.

[MCSmarties]

Duh...! *banging his head with a hammer*
StephanV, your post was a real eye opener!

I was completely wrong about what I understood as "bit rate".
What I really meant was something like "quality per pixel" or rather, compression factor.

Thank you so much for clarifying that issue for me!

The way I understand now, bitrate and resolution are something that go "hand in hand",
not parameters that you can tweak against each other.

So a discussion about "resolution vs. bitrate" is actually pointless!
The topic should be rather "resolution vs. compression factor" if anything...

:thanks:

[DeathTheSheep]

Just to make life more complicated (sorry ;)), the way you resize the video also plays a role in both compressability and visual quality. If you want to resize for plasma TVs which can pick up blocks easily, don't use lanczos or bicubic A=-1... a lot of ringing, less compressability, more blocks, etc (unless you want to pour in the necessary bitrate for all of the sharpened details)....
OK, look at this post I once made (*COUGHtodayCOUGH*): http://forum.doom9.org/showthread.php?p=719776#post719776
I think I hit some of the big points... :D

[oluv]

hello, i wanted to add my observations to this. i had to fight with the same problem. what's better resize or not resize when the bitrate gets low? and strangely i found that i had better results when i didn't resize, but rather encoded with original size.
here some screenshots. i encoded both with exactly the same bitrate (348kbps), whereas the first one was resized to 464x256 (size was automatically chosen by nero recode) and the other one was left original size 720x576
i took both screenshots from a full-screen view and then had to size them down again in photoshop not to exceed 200kb and to make them both the same size.

as you can see the unresized screenshot shows much more details and the compression artefacts are by far not annoying, the difference is even more pronounced when viewing full-screen! i was surprised by the good results nero AVC delivered when encoding with such a low bitrate.
i have still to make more tests with this, but as for now it seems that i will always leave resizing untouched.

[LordIntruder]

Please do not use dark scenes, it is very difficult to see differences. Thanks you.

Anyway here it looks like the bed has got better details but I don't use Nero so I can't say why you got this. Is it same in all scenes? I would say maybe at 500Kbits that dark scene got enough bitrate to still display many details at full size and of course if you resize you lose some. Therefore it is normal to get details at full size and less when you resize.

What I suggest: if you encode at 250Kbits, is the result identical?

[mgh]

There is a superstition that bits/pixel should be about 2. My experience reminds me of W.Somerset Maugham's quote(paraphrased). "The young must learn for themselves that all that they have been taught and all that they have been told and all that they have been taught are nothing but lies,lies,lies; and each new discovery is another nail driven into the body on the cross of life".
If you want to play full screen, it is better to experiment for yourself when you have kbps limitations. Higher resolutions with controlled smoothing may actually be much better. Use the slowest encoding mode available and two or three passes.