Guru
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497 Messages
PQ on U-verse -- 720p vs 1080i
I recall reading a post somewhere that someone mentioned the 720p sourced broadcasts look better than the 1080i sourced broadcasts on U-verse. I think the theory was the extra overhead of the 1080i resolution and that progressive sources compress better. I was wonderig if this was perhaps true?
I've made the observation that HLN HD has issues the pixelation with sudden graphic and camera fade in/outs. In watching similar things happen on ESPN I did not see the pixelation bursts that were happening on HLN.
A little wiki research shows that HLN is 1080i and ESPN is 720P.
SomeJoe7777
Expert
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9.4K Messages
14 years ago
I did a VOD HD bitrate measurement today with a Cinemax HD On Demand movie.
The MRTG-measured long-term average bitrate for HD VOD comes in at 7.4 Mbps. This is over 30% more bitrate than the standard live feeds.
If you want higher quality HD, I would definitely recommend watching a movie on VOD if available.
Note that this is a single test with a single movie, and that other movies or shows, including those from a different network other than Cinemax, may be different.
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michail77
Guru
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497 Messages
14 years ago
Thanks, that additional bitrate sure does make a major difference in PQ.
Unfortunately, I'm sure it would be difficult to get the live streams up that high, they'd cause issues on marginal lines and stream counts. AT&T would need more bandwidth on the back end. Also, total DVR record time would be impacted. However, I'd be happy to give up DVR space for some quality.
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cheer
Guru
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939 Messages
14 years ago
Purely speculation here...but could the higher bitrate on the VOD stuff be due to "pre-encoding" -- in other words, could the VOD stuff be encoded and stored on VOD servers, so that the encoding doesn't happen real time?
Nah, the more I think about it the less sense that makes.
Hmm.
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SomeJoe7777
Expert
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9.4K Messages
14 years ago
Actually, I believe that is correct. The VOD content is probably pre-encoded and stored on a hard drive array. VOD is also sent to the STB via unicast IP, using HTTP protocol as opposed to the live TV, which is multicast IP, using RTP/UDP.
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JefferMC
ACE - Expert
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35.3K Messages
14 years ago
Hm... that would imply fewer artifacts due to lost packets due to the built-in retry mechanisms in TCP/IP.
It would also imply that some of that increased bandwidth is TCP/IP protocol overhead vs. the usually slimmer UDP.
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SomeJoe7777
Expert
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9.4K Messages
14 years ago
TCP header size is 20 bytes vs. UDP header size of 8 bytes, so there's only an additional 12 bytes using TCP. That's < 1% for 1500-byte packets.
Though TCP does provide for error correction, if the retransmission is too late, then the STB will have no choice but to drop the packet because that portion of the video stream will have already been processed. I suspect the STB has a large buffer for VOD to make up for this, probably on the order of 5 seconds or more as opposed to 1-2 seconds for live TV.
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bjtheman1
Tutor
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9 Messages
14 years ago
Until I read this post I never checked what my system aspect ratio was on, and I'm very happy now. I have 3 plasma's all of them are 720p and I switched the aspect ratio to that yesterday. WOW, picture looks amazing now.
thanks
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