PQ on U-verse -- 720p vs 1080i

Here're some SomeJoe (he authors and edits HD material) posts on the subject:

http://forums.att.com/t5/TV-Programming/World-Cup-HD-picture-quality-just-as-poor-as-superbowl-and-other/m-p/2047827#M8110

http://forums.att.com/t5/Equipment/720-or-1080-Installer-told-me-that-720-is-more-reliable/m-p/2203785#M28730 😉

Chris

Please NO SD stretch-o-vision or 480 SD HD Channels
1-866-465-1496 for direct TS to avoid Mr. Voice recognition
Your Results May Vary, In My Humble Opinion
I Call It Like I See It, Simply a U-verse user, nothing more

I gave those a read over but I don't think that addresses what's going on at encoding time.  

I see numerous comments about Dish's PQ being so much better than U-verse.  The interesting thing is Dish supposedly down converts 1080i to avoid compression issues within the allocated bandwidth.  The theory being reduced compression issues are better than a messy higher resolution picture.

Maybe he'll pop in here later to give you his detailed take on the subject.

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@michail77 wrote:

I gave those a read over but I don't think that addresses what's going on at encoding time.  

 

I see numerous comments about Dish's PQ being so much better than U-verse.  The interesting thing is Dish supposedly down converts 1080i to avoid compression issues within the allocated bandwidth.  The theory being reduced compression issues are better than a messy higher resolution picture.

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Thanks, SJ, for popping in with your wisdom.

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@SomeJoe7777 wrote:

The picture quality (i.e. artifact level) is dependent on the bitrate and the complexity of the source material.

 

A 1080i source is more complex than a 720p source, both because there are more pixels to encode (62.2 Mpixels/sec for 1080i vs. 55.3 Mpixels/sec for 720p), and because interlaced video is inherently more difficult to encode than progressive material (there are less opportunities to use accurate motion prediction).  To get the same artifact level (picture quality) for 1080i, you need about 20% more bitrate (about 10% for the additional pixels and another 10% to make up for the difficulty of interlaced video).

 

But, most providers, U-Verse included, do not make special consideration for 1080i material.  On U-Verse, both 720p and 1080i material are encoded and transmitted at 5.7 Mbps.  This is why the 1080i material doesn't look as good as it could.

 

If the bitrate for 1080i were upped to 6.8 Mbps, it would look (artifact-wise) as good as the 720p material.

 

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This is the most coherent answer to the PQ questions I've seen on these boards.  Somehow, resolution became everyone's standard for quality.  It simply isn't the whole story.  I really wish manufacturers and service providers would quit confusing people by marketing purely based on resolution.  High bitrate is the reason Blu-ray looks better on a 1080i set than a 1080i signal from U-Verse. 

I want to puke every time the subject of 1080p comes up around here.  Subscribers think that the reason their HD isn't as good as it should be is because it's not 1080p.  HD is such a cool technology.  Too bad bandwidth limitations leave it somewhat neutered.

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@SomeJoe7777 wrote:

The encoders that AT&T are using for U-Verse are the Motorola SE-5100 units, and they're using the constrained fidelity (capped VBR) mode.  The H.264 output from these units isn't the best MPEG-4 you can get, because these encoders don't implement all features of the codec, but they perform quite well anyway.

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I looked at the Motorola SE-5100 specs. It mentions "Main Profile Encoding" for HD services, but I didn't see "High Profile Encoding" anywhere on this model. I don't see why a provider would need to skimp on that. Do you think we would see a noticeable improvement they switched to High Profile? As far as I've known, Main Profile is generally not supposed to be used for HD content. I mean even a quick read on Wikipedia for H.264's Main Profile states "It is not, however, used for high-definition television broadcasts, as the importance of this profile faded when the High Profile was developed in 2004 for that application."

Thanks, that confirms what I was noticing with my eyes.  

The irony is most satellite providers down convert the 1080i signals to lower interlaced resolutions.  So it seems odd to me that most non OTA broadcast channels choose to go 1080i.  The slight advantage 1080i has in resolution is getting killed by compression.

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@chrisw wrote:

 

I looked at the Motorola SE-5100 specs. It mentions "Main Profile Encoding" for HD services, but I didn't see "High Profile Encoding" anywhere on this model. I don't see why a provider would need to skimp on that. Do you think we would see a noticeable improvement they switched to High Profile? As far as I've known, Main Profile is generally not supposed to be used for HD content. I mean even a quick read on Wikipedia for H.264's Main Profile states "It is not, however, used for high-definition television broadcasts, as the importance of this profile faded when the High Profile was developed in 2004 for that application."

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The main profile is used vice high profile to reduce decoder complexity.  This enables a lower cost and lower complexity decoder chip to be used in the DVR/STB units.

However, truth be told, the decoder used in the U-Verse STBs (the Sigma Designs 8634) is quite capable of decoding high profile without any issues, so I don't see a reason that they couldn't use encoders that do high profile at a later date.

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@SomeJoe7777 wrote:

...

 

If the bitrate for 1080i were upped to 6.8 Mbps, it would look (artifact-wise) as good as the 720p material.

 ...

 

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This probably isn't the best comparison as I'm sure there are some differences between real-time encoding and VOD.  However, the premium  HD VOD seems to run somewhere around 6-7 Mbps (through the RealTime app) and comparatively looks great.   Any idea what the VOD specs are?