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sofakng3

join:2007-08-25
Kingston, PA

Does Comcast use 3 or 4 channels per QAM? (MPEG2 bitrates)

Does Comcast (in Northeastern PA, or in general) use 3 or 4 HD channels per QAM?

I'm switching to Dish to Comcast and I've been able to capture a lot of raw MPEG-TS streams from Dish and I'm looking forward to the bitrate comparisons between the two.

In general, Dish is using around 4 - 6 Mbps (MPEG-4) and the last I checked Comcast is around 12 Mbps (MPEG-2).

In general, I'd think that Comcast should have a slight edge due to the 2x - 3x bitrate but I'm not sure...?

Os

join:2011-01-26
US
For most QAM maps of Comcast that I've seen, it's either 2 HD with some SD interspersed or 3 HD per QAM. This may vary by region.


telcodad
Premium
join:2011-09-16
Lincroft, NJ
kudos:17
reply to sofakng3
While someone like DrDrew See Profile or cypherstream See Profile would probably know the latest on that, this is what it says (from 3 years ago) in the Comcast Cable TV FAQs section: »Comcast Cable TV FAQ »What are the national 3:1 HD muxes from Comcast?

SpHeRe31459
Premium
join:2002-10-09
Sacramento, CA
kudos:2
reply to sofakng3
said by sofakng3:

In general, Dish is using around 4 - 6 Mbps (MPEG-4) and the last I checked Comcast is around 12 Mbps (MPEG-2).

In general, I'd think that Comcast should have a slight edge due to the 2x - 3x bitrate but I'm not sure...?

That's faulty logic, MPEG2 is an older and far less efficient compression algorithm than MPEG4/AVC (H.264). So you cannot directly compare bitrates.

andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL
reply to sofakng3
Most national channels are 3:1 with variable bitrates constantly shuffled between them. Some sports channels are only 2:1. Local broadcast can vary, but are typically 2:1, since they are typically just passed on as received. It could seem more than 2:1 as the broadcast subchannels are often included on it's frequency. (For ref, the typical 256QAM used for cable TV has double the bandwidth of the 8VSB used for broadcast.)

sofakng3

join:2007-08-25
Kingston, PA
reply to SpHeRe31459
Oh, I know that MPEG-4 can't be compared to MPEG-2 directly but in general I would think that MPEG-2 at 3x the bitrate should look better than MPEG-4. MPEG-4 completely beats MPEG-2 at low bit-rates though.

Although, MPEG-2 over-the-air (ATSC) is 19 Mbps and looks much, much better than MPEG-4 at 5 Mbps (i.e. Dish Network).

Therefore, I'm wondering how MPEG-2 at 12-14 Mbps would look against MPEG-4 at 4-6 Mbps...

sofakng3

join:2007-08-25
Kingston, PA
reply to sofakng3
Yeah, 3 HD channels in QAM256 (38 Mbps) seems pushing it even with dynamic bitrate allocation but 2 HD + SD I'd think is OK.

Once my installation is finished I'm going to check actual bitrates with TSReader and my HDHomerun to see what exactly Comcast is pushing out in my area. Should be interesting

andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL
In general, most of the national channels are actually processed at a site in Colorado, then distributed to not only Comcast, but to other cable companies, too. That's why you'll typically see the same 3 channels bundled together across the country on Comcast systems.

Also, the source may not always be the best either. Satellite bandwidth is tight and expensive. Some channels may highly compress their master feeds to make the most of that bandwidth, too.


motorola870

join:2008-12-07
Arlington, TX
kudos:4
Reviews:
·Time Warner Cable
said by andyross:

In general, most of the national channels are actually processed at a site in Colorado, then distributed to not only Comcast, but to other cable companies, too. That's why you'll typically see the same 3 channels bundled together across the country on Comcast systems.

Also, the source may not always be the best either. Satellite bandwidth is tight and expensive. Some channels may highly compress their master feeds to make the most of that bandwidth, too.

I find it interesting how TWC does their HD channel packaging with SDV:

3:1 HD QAM
2 HD and 2 SD QAM
2 HD and 3 SD QAM
1 HD and 6 SD QAM

these are the variations TWC has with SDV and HD channels.


cypherstream
Premium,MVM
join:2004-12-02
Reading, PA
kudos:3
Reviews:
·ProLog
reply to sofakng3
It's for the most part 3:1 QAM now.

Some cable systems receive AMC Networks 4:1 however. AMC Networks broadcasts:
AMC HD
IFC HD
We HD
Fuse HD

All in one MPEG2 transport, traffic shaped to 38.8 mbps to fit in one 4:1 compressed QAM.

I know a few providers that have a handful of 4:1 compression, but last I've heard Comcast generally uses 3:1 compression.

Going MPEG4 would improve this rate to 5 or 6 HD per QAM.


sofakng

@ssa.gov
Interesting... thanks for that information.

Since you are near my location (i.e. I'm in Wilkes-Barre, PA), have you compared Dish Network and Comcast?

Right now I have both and Comcast is definitely sharper in almost all cases, but has more mosquito noise and macroblocking. I don't think the macroblocking is always Comcasts fault because Dish shows it as well but because of the MPEG-4 compression it isn't that visible.

I'm still a bit torn on which I'll keep but both are good and bad...

kb1

join:2008-11-15
South Bend, IN

1 edit
reply to cypherstream
said by cypherstream:

It's for the most part 3:1 QAM now.

Some cable systems receive AMC Networks 4:1 however. AMC Networks broadcasts:
AMC HD
IFC HD
We HD
Fuse HD

All in one MPEG2 transport, traffic shaped to 38.8 mbps to fit in one 4:1 compressed QAM.

I know a few providers that have a handful of 4:1 compression, but last I've heard Comcast generally uses 3:1 compression.

Going MPEG4 would improve this rate to 5 or 6 HD per QAM.

But would HD picture quality suffer going to MPEG4 and 6HD per QAM?


cypherstream
Premium,MVM
join:2004-12-02
Reading, PA
kudos:3
Reviews:
·ProLog
IMO, AMC Networks do look a little more grainy and the picture is riddled with mosquito noise and micro blocking from a close up view.

At normal viewing distances, it just appears to me like the grain on a film... which is something we've all been used to from going to the movies. Not bad, I don't mind that effect... just don't sit too close to the TV when watching these 4 channels (AMC, Fuse, We, IFC).

Supposedly newer encoders are more efficient and can lessen the picture degradation.

AMC Networks appears to be moving their networks to a new satellite in November that will help with their excess compression and lossy quality.