There are multiple levels of compression. What typically happens here in the USA is that your local TV station gets, via satellite, a "master feed" which typic

There are multiple levels of compression. What typically happens here in the USA is that your local TV station gets, via satellite, a "master feed" which typically is very high bitrate Mpeg4. It then converts it to Mpeg2 (which requires a higher bitrate for the same quality), and compresses it to fit into its 19Mb/s ATSC 8VSB broadcast standard. If your local broadcaster has no subchannels, then you win(1). The network show gets all 19Mb/s of bandwidth. However, if your local station has many subchannels (eg, 24hr weather, local news, re-runs of shows from the 1950s, etc), then they all share that 19 Mb/sec and you get far less than 19Mb/s allocated to the network show (especially when there is a lot of motion on the subchannel). The worst I've seen is some ABC affiliates who actually had a SECOND "HD" subchannel for the "livewell" network, which made their network programming look horrible. I put up a bigger antenna to pull in ABC from a neighboring market & avoid a local affiliate that was doing that. Your local cable company picks up the MPEG2 broadcast and if you're lucky, it just passes it through (re-muxing it into a 38Mb/s QAM subchannel). If you're unlucky, it takes the already compressed MPEG2 stream and compresses it harder. Back in the "good old days", the network satellite feeds were not encrypted, and people with the right equipment (Big Ugly Dishes) could pick up the raw network feed, which was reportedly awesome. (1) That is, you win if the equipment doing the MPEG4 -> MPEG2 transcoding doesn't suck. I've consistently seen stations that have a lower bitrate but better quality due to newer encoders doing things like adding repeat field flags to telecined film content, so your mileage may vary.