Mbits/s or resolution?

[pascal]

Sorry for this quick post. I will elaborate more latter.

My question is why people worry so much about resolution (between 1080p or 720p) when we will be pretty much bandwith (Mbits/s) limited? I mean, most 720p content (files from internet) I saw was 8MBits/s which is not much for 720p. With a good compression rate of 50:1 we could go as high as 27Mbits/s (edited: with 720p).

Maybe one of the HDTV or Information Theory Gurus could explain that to me.

Thanks

 

[breez]

In internet there are obviously bandwidth constraints, but the question is more relevant with HDDVD/BluRay. Those should have the bandwidth necessary for 1080P content.

 

[RussSchultz]

720p looks just fine in the terrestrial broadcast retraints of 19Mbps (and, generally, that whole 19Mbps isn't used by the primary stream).

MPEG4 will be about twice as good (or better) given the same bandwidth.

One of the problems with content from the internet is:
-usually captured analog
-converted (or transcoded) to MPEG4 using encoders that aren't the best and are more tuned for speed rather than quality. Because of that, the bitstream is larger for the same perceived quality.

An interesting fact: original DVDs were up the 5-7 Mbps range. These days, the encoding technology and algorithms have gotten so much getter that its usually 2-4Mbps for the same quality.

 

[pascal]

In internet there are obviously bandwidth constraints, but the question is more relevant with HDDVD/BluRay. Those should have the bandwidth necessary for 1080P content.

I have my doubts about that. Probably most movies we will see will be in the 10~12GBytes range for 100~160 minutes content. Probably most content will be in the 8~16Mbits/s which will be below the 50:1 for 720p (27Mbits/s).

 

[pascal]

720p looks just fine in the terrestrial broadcast retraints of 19Mbps (and, generally, that whole 19Mbps isn't used by the primary stream).

MPEG4 will be about twice as good (or better) given the same bandwidth.

One of the problems with content from the internet is:
-usually captured analog
-converted (or transcoded) to MPEG4 using encoders that aren't the best and are more tuned for speed rather than quality. Because of that, the bitstream is larger for the same perceived quality.

I understand. Thanks Russ.
But even 19Mbps is below some 27Mbps (50:1 compression), so my guess 720p or 1080p will not be different in terms of image quality (edited: with low Mbps).

An interesting fact: original DVDs were up the 5-7 Mbps range. These days, the encoding technology and algorithms have gotten so much getter that its usually 2-4Mbps for the same quality.

I have noticed that too. I have some DVDs copies (made with DVDShrink) which are in the 2.4Mbps range. The quality is very good.

edited: The DVD resolution is 720x480. Then the 720p has 3:1 more pixels than DVD. To keep the same image quality we will need something in the 6~12Mbps for the 720p.

 

[breez]

the 50:1 for 720p (27Mbits/s).

I take it that you calculated that with 60 progressive frames per second at full 24-bit precision. I think 24 fps more relevant for film content and depending on colorspace you save more bandwidth. DVDs use YV12 which is 12-bit.

 

[pascal]

Yes I calculated with 60fps and 24 bit. Using your information then the 8Mbps is close to 50:1 with 720p when thinking in terms of DVD standards.

But let me rewrite my question:
If we have a movie with 12Mbps will it be visually much better with 1080p than 720p?

 

[RussSchultz]

Yes I calculated with 60fps and 24 bit. Using your information then the 8Mbps is close to 50:1 with 720p when thinking in terms of DVD standards.

But let me rewrite my question:
If we have a movie with 12Mbps will it be visually much better with 1080p than 720p?

Depends.

 

[kyleb]

Yeah, given the same bitrate the higher resolution obviously has the opportunity to provide a sharper picture but it also runs more of a risk of compression artifacts showing up during complex screens with fast movement. So which will look better comes down specificly to what is being shown.

 

[pascal]

I agree, but my guess most content will be fast-action or mixed content video.

I downloaded a nVidia purevideo demo (wm9, 720p, 8Mbps video, 256kbps audio, 2:16 min, 128MB) and it looks very good