ATSC 1.0 MPEG-4 older TVs no video
In 2008 the ATSC ratified the MPEG-4 TV broadcast standard. Numerous ATSC 1.0 TVs were sold before this standard was ratified, and still operate today. TV manufacturers continued to make some non-MPEG-4 TVs for a decade after the standard was ratified. As a practical matter to avoid abandoning viewers with older receivers, ATSC 1.0 broadcasts remain on while implementing ATSC 3.0 broadcasts. This lighthousing of ATSC 1.0 broadcasts leads broadcasters to use MPEG-4 encoding for ATSC 1.0 broadcasts.
MPEG-2 is the legacy encoding standard for ATSC 1.0 broadcasts, which any old DTV can receive. A typical ATSC 1.0 MPEG-2 broadcast channel layout was one 1080i channel and several 480i channels, or 1-2 720p channel(s) with even more 480i channels. ATSC broadcast channel layout is a tradespace between the number of subchannels vs. the bandwidth per subchannel. This database lists the channels available in a given area. Click “Technical Data” to see the resolution and encoding of each channel.
As ATSC 3.0 broadcasts roll out, the number of ATSC 1.0 channels will decrease. A mitigation for broadcasters is to switch to MPEG-4 encoding for the ATSC 1.0 broadcasts, which is more efficient than MPEG-2 and allows packing more channels into the same transmitter bandwidth. This leaves older TVs and receivers with audio-only on MPEG-4 channels. This MPEG-4 list is missing some broadcasters. Note that some ATSC broadcasts have audio-only subchannels.
A solution for the end user lacking an MPEG-4-capable TV is to buy an ATSC receiver box that supports MPEG-4. These can be obtained for less than $50. ATSC 3.0 receivers are available for less than $100 if desired to access ATSC 3.0 broadcasts not available even on some new TVs.
Enthusiasts make their “band scan” data available for TV and FM radio typically using a Raspberry Pi to enjoy and share the hobby of broadcast DXing.