In case this has escaped one's notice, Comcast is currently in the process of changing the compression method for HD channels from MPEG-2 to MPEG-4. They are doing it in several regions at a time.
The potential advantages of MPEG-4 over MPEG-2 are:
- Improved picture quality. (That is what Comcast is claiming, though it depends on just how much over-compression they do.)
- A recording on the DVR will take less space. I have seen numbers like being able to store 2 to 3 times the amount of HD content (so if one could record up to 60 hours of HD content, if the channels have been changed to MPEG-4, it would be 120 to 180 hours of HD content).
- It frees up cable bandwidth for DOCSIS 3.1 and much faster Internet speeds. (Comcast isn't outright advertising this one to the TV customers, but it is being mentioned in other places.)
- It gives marketers a new buzzword. In this case, redeploying an HD channel with MPEG-4 is what Comcast advertising is calling "HD Enhanced", and what I am calling "the HD picture quality we should have been getting".
The disadvantages of going to MPEG-4 for HD are:
- Old CPE (customer premises equipment, i.e., Comcast boxes in our homes and businesses) may have to be replaced if those CPEs don't decompress MPEG-4.
- Incompatible customer equipment (such as some models of Tivo and other DVRs) may have to be upgraded or replaced.
Comcast is converting a few regions at a time. This is a list of areas that have already started the transition (courtesy of https://support.tivo.com/articles/Fe...Select-Markets
- Central, CA
- Fresno, CA
- Sacramento, CA
- Champaign, IL
- Chicago, IL
- Springfield, IL
channels are being moved to MPEG-4; the SD
channels will continue on MPEG-2. If you do not
have HD service (that is, you have SD-only service,
or you watch exclusively SD channels), you will not be affected.
Also, I have seen conflicting information on whether local
HD channels will remain MPEG-2 or will be recompressed using MPEG-4. (I have seen second-hand reports go both ways, but I haven't yet seen an official Comcast announcement clarifying this.)
There is already a lot of Comcast equipment in people's homes that can already handle MPEG-4: all X1 boxes, all RNG150 and RNG200 boxes, and there may be others. (The RNG* designation is Comcast's relabeling the front of the box, e.g., the HD DVR I have shows "RNG200N" on the faceplate, but the FCC sticker on the bottom identifies it as a Motorola DCX3501.)
This is what should be happening in an area that is currently being upgraded: if Comcast records show that you have an incompatible box, there should be a note in your monthly statement, and you should also receive a separate letter. The letter will also direct you to http://www.xfinity.com/hdenhanced
(which appears to be a generic site since you can look at it without being logged in, and the date shown there doesn't seem to be tied to either your region nor to your account, and it doesn't really say anything that isn't already in the letter).
When the box swap is available in your area, channel 1995
should appear in your lineup. (Here in Salem, which is an hour's drive south of Portland, Oregon, channel 1995 is labeled "Enhanced Service Check".) When channel 1995 is active, if you tune each of the Comcast-provided HD box to 1995, it will check that box and either tell you "This set-top box is good to go!" or give you a message that the specific box needs replacing. If it needs replacing, self-install kits can be acquired for free (either by stopping at the Xfinity store or by requesting a box shipment) and the old box should be returned within 30 days. (Having an installer comes out will cost money.) Equipment swaps will be for similar-functioning equipment (e.g., an HD DTA for a MPEG-4-compatible HD DTA, or a HD DVR for a MPEG-4-capable HD DVR) and should not
affect your monthly bill.
Note: Channel 1995 works only for Comcast-provided boxes; for third-party boxes (e.g., Tivo), this check won't work (e.g., screen goes blank) and you would have to consult the vendor to see if your box is compatible (e.g., the Tivo article
I quoted from, which lists compatible and incompatible Tivo models after the section that lists the regions currently affected).
CableCARDs are compression-agnostic, it is up to the device they are plugged in to handle MPEG-4 compression, such as a Tivo, a CableCARD-ready TV, a tuner card in a PC. Again, Channel 1995 won't work and won't tell you whether or not the specific device is compatible unless the specific device is a Comcast-provided HD box. It wouldn't surprise me if there are some people on this forum who have a CableCARD in their TVs and find out that their TVs don't have the ability to decompress MPEG-4 so they end up having to buy or rent a box to continue watching shows in HD. (I don't think all CableCARD capable TVs also had MPEG-4 decoders.)
If you are in a Comcast area that is not
currently switching over to MPEG-4 and channel 1995 is not available
in your lineup, the equipment swap will not
be available at that time.
Note: if you have a Comcast-rented HD DVR that is incompatible and thus will need a box swap, keep in mind the recordings and schedules in the DVR will not
transfer over to the new box. Even if you had supplied an external disk for the DVR, the programs will not play if you connect that disk to another DVR. When my previous RNG200N HD DVR died, I did a mixture of Video-On-Demand, catch re-broadcasts, go to the networks' sites for online viewing of past episodes, and in a few cases there was no choice but to do without. With the equipment swap, at least one can attempt to catch up on at least the shows and movies that aren't available by other means to minimize what one permanently loses with the equipment swap. I have seen the suggestion that one could "play" various shows to a VCR or to a DVD recorder to save them, but my concern would be whether copy protection would be active on the output of the DVR and prevent the VCR or DVD recorder from recording that program.
My expectation is that when Comcast starts moving HD channels from MPEG-2 to MPEG-4, it will be a few channels at a time, so those with incompatible equipment might notice a few HD channels becoming incompatible or unavailable, followed a few days or a week later by a few more HD channels unavailable, maybe over the course of 2 to 4 months. And, if one is using Comcast boxes, the channel numbers would probably remain mostly unchanged, even though behind the scenes the HD channels are probably moving from one QAM and subchannel number to another QAM and subchannel number. The cable boxes seem to be good at hiding these messy details, but some equipment might not be so good, e.g., a TV that has a CableCARD and can decode MPEG-4 may have to rescan to find new real channel / subchannel numbers of one's favorite channels, whether or not they maintain the original virtual channel numbers. I don't know how other equipment, such as Tivo, handle these messy details.