MPEG-4 Subchannels

Intro
The digital TV broadcast standard we currently use, ATSC 1.0, was written in 1993 – nearly 20 years ago. The original standard calls for the use of the MPEG-2 video compression codec. As such, 100% of all TVs and other equipment capable of receiving ATSC 1.0 are capable of decoding MPEG-2 video.

 

Modern video compression codecs, such as MPEG-4 (ie, H.264) and H.265 (also known as HEVC), use a lot less digital bandwidth to convey the same quality picture as MPEG-2. Said another way, newer codecs are much more efficient than MPEG-2. Internet-based streaming TV platforms almost universally use the aforementioned newer video codecs. As such, smart TVs (ie, the majority of TV sets sold in the last 10 years) are capable of handling these newer codecs.

Implementation and compatibility
Some broadcasters are beginning to broadcast subchannels encoded in MPEG-4, as a way to make more efficient use of their allotted bandwidth. On many newer TVs, these subchannels will decode just fine and the TV will most likely give no indication whether the picture being decoded is MPEG-2 or 4. On older sets, however, these subchannels may appear as “Audio Only” or, potentially, some other message.

Upgrading to a newer TV set is, indeed, one option. We have also found that the generic ~$30 tuner boxes, such as those sold under the GPX, and Mediasonic names (available at Menards, Amazon and other retailers) are capable of decoding MPEG-4 subchannels – and can be connected to nearly any TV, projector or monitor in existence.

 

Please note that, while MPEG-4 capability is widely implemented in newer sets, it’s a feature that’s not well-documented. We are still trying to determine, for instance, which DVR systems are compatible and which ones are not, etc. See: MPEG 4 Device Compatibility List – AVS Forum

MPEG-4 subchannels (by market):
Twin Cities:
23.10 Comet (simulcast in MPEG-2 on 23.2)