Cable HFC Bandwidth Limits Are Hurting Video Services, Too

Last week I had a series of posts about how Cable Hybrid Fiber Coax is disadvantaged versus Fiber-to-the-Home systems like Verizon FiOS, especially in the long run.  I speculated that it might take Cable six years to bite the bullet and start replacing the coax parts of their system with Fiber-to-the-Home, due to competitive pressures to match the higher bandwidth rates available from all-fiber systems.  Meanwhile, Cable will be living with a disadvantage that will show up in both video services and internet access services.

While it might take six years (give or take a few) for Cable to cave, it is worth pointing out that Cable is being forced to compromise quality already in very visible ways, due to the bandwidth limitations on their HFC plant.  Nyquist Capital's blog pointed me to an excellent post on the Audio Visual Science Forum about how Comcast is starting to compress HD video channels in order to fit more channels into less bandwidth.  Basically, Comcast's video compression allows them to fit three HD channels in the space that two channels used to occupy. 

The quality difference between a compressed Comcast HD video channel and an uncompressed FiOS  HD video channel is pretty obvious when you view screen shots, side by side.   There are lots of good examples on the AV Science Forum post, but here is one example:

FiOS uncompressed HD screen shot from Discovery Channel:

Comcast compressed HD screen shot from Discovery Channel:

Cable companies are lucky that they don't compete against FiOS in very many places, yet.  Instead, Cable's main video competition is Satellite TV, which also compresses their MPEG-2 channels.  If cable companies were competing with FiOS in more places, it would harder to get away with selling an inferior product. 

Comments

[Ike Elliott]

Thanks, Michael, that's very helpful. Great details!
Ike

[Michael Graves]

Ike,

You are dead right on this matter. However, there is a little issue of semantics. All HD broadcasts are compressed to start. They're compressed to 19.2 Mbps MPEG-2 according to the US ATSC standards. That's what you receive off-air. That's the best you'll ever see from a broadcaster, at least for now.

Cable companies and satellite providers "rate shape" their HD transmissions to provide more HD channels on their limited bandwidth transmission systems. They may reduce the data rates to less 10 Mbps, and they can vary the data rate channel by channel or even program by program in some cases.

Some carriers may transcode the program streams into H.264/MPEG-4 format if their set-top boxes can decode such material. MPEG4 is about twice as efficient as MPEG-2, meaning that 10 Mbps MPEG-4 can look as good as 19.2 Mbps MPEG-2.

This also is part of how Apple TV get decent looking HD movie downloads from a a device that internally limited to only 8 Mbps. It uses H.264 and 720p for all movies to meet its bandwidth limits. No 1080i downloads, even if the device output is scaled and presented as 1080i.