HELP - MPEG2 Stations Consistently Unwatchable

Reception, channel detection, network issues, CableCARD setup, etc.
dcburnquist
Posts: 13
Joined: Mon Feb 13, 2017 9:23 pm

HELP - MPEG2 Stations Consistently Unwatchable

Postby dcburnquist » Fri Jan 11, 2019 3:49 pm

To keep a long story short, the few stations (CBS, FOX, WGN, Weather) that are still delivered in MPEG2 format from Comcast are giving us major headaches. We are using an HDHR Prime.

We watch a lot of the late night talk shows and I can't remember the last time any of them were watchable whether live or recorded. It's not any better - and in some cases worse - than a poorly placed antenna. Signal strength and quality is at or near 100% consistently. Every time we have a 'glitch' I can see a drop from the high 14-18mbps stream down to between 2-5mbps for whatever reason. Again, all MPEG4 channels come in fine, but the few that are MPEG2 are giving the HDHomerun fits when trying to stream. This does not happen 100% of the time, but it's an excessive amount of times throughout the day and of course whenever we actually have a show we're trying to watch.

Please help. We've just accepted it for many months, but I'd like to find an actual solution to a problem that I would like to think shouldn't exist.

rpcameron
Posts: 736
Joined: Fri Mar 25, 2016 9:55 am

Re: HELP - MPEG2 Stations Consistently Unwatchable

Postby rpcameron » Fri Jan 11, 2019 8:42 pm

Sounds like a network bandwidth issue if it's only higher bitrate MPEG2 streams. What is your network topography/layout?

gtb
Expert
Posts: 3799
Joined: Thu Oct 06, 2011 1:00 pm
Location: Sunnyvale, CA USA

Re: HELP - MPEG2 Stations Consistently Unwatchable

Postby gtb » Sat Jan 12, 2019 8:29 am

Please help. We've just accepted it for many months, but I'd like to find an actual solution to a problem that I would like to think shouldn't exist.
I am pretty sure you should be working with Comcast on this. I have seen this on a colleagues T-vendor device using Comcast too (although I have not done any research in their environment), so it is likely not a SD issue to be fixed by them (this is a GIGO problem).

It almost certainly will depend on the market regarding what specific channels they put together, but Comcast muxes various OTA stations on each physical transport channel, and there is only 38Mb/s to fit all the content they are trying to fit (all the stations, OTAs and national, are transcoded to fit into specific bitrates to be able to fit into their specific transport channels). The equipment they use to perform the various transcoding and muxing have various bitrate min/max/target/priorities for each stream, and it is possible the settings are less than optimal for the specific channels they are trying to put together for the OTAs in your specific market.

One thing that would be interesting to start is to record the raw stream on the same QAM channels as one of your OTA using your favorite tool (hdhomerun_config ... save can do it) and see whether the issue is bitrate contention (you can't fit 50Mb/s into a 38Mb/s QAM), or whether their encoder is simply choosing to limit the channels of interest during some period. You will likely then want to use a stream analysis tool to do the analysis. For quick looks, I have tended to use (free) open source tools like DVB Inspector and look at the bitrate graph (but to see such things visually you are going to need to filter to a very specific small time range, as averages for large time ranges will hide the bad (and good)). That will likely show your OTA stream(s) getting bit starved during some magic transition point. This helps you understand what it going on, and what the best data to collect and present will be.

In order to provide the necessary information for the next steps you are going to need to capture both the raw transport stream, and each and every decoded program on that stream (all at once), in order to be able to provide the detailed information to present your case to Comcast. You should collect all your streams, align them with the same timestamps, and also show the visual artifacts as part of your case. And here is where it is going to get very very very hard (you thought it got easier along the way?), because you will eventually need to get that data to the local Comcast TV engineering team (no CSR or Tech has any clue about the encoders). So it will require a lot (lot, lot, lot) of time and perseverance, which as likely as not will include multiple visits by a tech (Comcast customer support representatives tend to only know how to send techs ("shibboleet" does not work at Comcast)) just so it can eventually get escalated.

If you do not have the ability, or interest, or resources, to deal with the details at this level, you could try an alternative and to take it to the Comcast forums (for all I know there are already complaints there), and get anyone else that sees the same things (in *exactly* the same market, with *exactly* the same channels; generic comments from others in other markets and other channels are not only useless, they will contribute to the entire topic being dismissed as a random flailing which should be ignored) to add to the case, and hope someone in Comcast sees the issue, and wants to take ownership of understanding/addressing this. As you may know from other forums, trying to keep a discussion strictly on-topic is another full time activity.

It should be noted that in some markets Comcast has reported to have started transcoded even the local OTAs into MPEG4 720p (they did that nationally for the "cable" channels, but left the local OTAs in whatever format it was previously, while still transcoding to the bounded bitrate they require). If/When they do so for your market this issue may be different (it is even possible that what you are seeing is a transition point artifact, where they first got some new transcoding/muxing hardware in place to prepare, and the current setup is not intended to be long term).

Good luck.

rpcameron
Posts: 736
Joined: Fri Mar 25, 2016 9:55 am

Re: HELP - MPEG2 Stations Consistently Unwatchable

Postby rpcameron » Sat Jan 12, 2019 9:38 am

I believe the OP is the same as on the Channels forum. If so, the problem is not related to Comcast at all, but rather his wireless and mesh wifi setup. I believe he's been directed to the proper solutions.

asauers
Posts: 96
Joined: Thu Aug 25, 2016 11:03 am

Re: HELP - MPEG2 Stations Consistently Unwatchable

Postby asauers » Mon Jan 14, 2019 7:00 am

To keep a long story short, the few stations (CBS, FOX, WGN, Weather) that are still delivered in MPEG2 format from Comcast are giving us major headaches. We are using an HDHR Prime.
Do you use wemo mini smart switches? Does the "glitch" happen at a specific interval (like every 10 minutes)?


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