The encrypted message you received is not DTMB, but DMB-H or CMMB. The promotion of terrestrial digital TV in China is divided into two stages and two sets of standards.
Before the Beijing Olympic Games, terrestrial digital TV has been launched, using DMB-H scheme, MPEG-2 and H.264 as coding, ACC and MP3 as audio coding.
Both are international common standards. And from the beginning, the mode of encrypted charging was adopted. This scheme introduces HD mode for home TV respectively.
(only launched in a few cities such as Beijing) and CMMB mode of mobile devices. Due to the cost and patent reasons, it has not been widely promoted.
Only CMMB has formed a certain market because it is used for rural household registration. Soon after, China began to formulate its own terrestrial digital TV standard DTMB.
Coding adopts S+ (pre-S, incompatible),
The audio coding adopts DRA, which is played by clean stream for free. It has become a new national standard for terrestrial digital TV and is listed as one of the four major standards in the world by ITU.
DTMB terrestrial digital TV has been piloted in Hunan since 20 13. 20 14 requires that the newly listed TV sets of 40 inches and above must directly support the reception of this standard.
In other words, you don't need a set-top box, and you can watch it directly with an ordinary ground wave antenna. However, there are still a large number of TVs on the market that do not support the sound of the new national standard.
In many places, DTMB terrestrial digital TV transmission tower has just started construction and has not been put into use, so in some places, only encrypted terrestrial wave channels can be found.
Charge for DTMB
In addition, it is not excluded that some TV manufacturers that focus on network TV function deliberately block DTMB signals.
Hisense's 20 14 42-inch TV can only find CMMB signal, and Sony's 20 12 all-in-one can find DTMB signal.
Only sound without image is understandable, and S+ was not supported at that time.