Misunderstanding of the ``worst sub-channel'' that erupted at the Olympics Care must be taken when using the ``Zenroku Recorder''

"Sub-channels are the worst. I was surprised by the poor quality."

When I heard that from an acquaintance who was watching the broadcast of the Tokyo Olympics, I felt that I might have to change my mind. After researching it, it seems that there are quite a few people who feel the same way.

On the other hand, the writer was in the mood of "thank you for operating the subchannel", so it is in contrast. This is because, before digital broadcasting, the time of the news was inserted in the middle of the broadcast.

In the days of analog broadcasting, only one program could be sent to one channel (radio band available for broadcasting), but in digital broadcasting, data transmission is managed in units called "segments". It is now possible to utilize

In other words, I was able to continue watching the Olympics live because of the existence of the sub-channel function.

Reason for poor sub-channel image quality

The question is how much the image quality drops. In the case of terrestrial digital broadcasting, 1440 x 1080 pixel images are broadcast in 12 segments. By allocating part of this to sub-channels, it is possible to continue broadcasting the live Olympics while broadcasting the originally planned broadcast as it is.

It is possible to choose how to divide and what quality to send, but in the case of the Olympic broadcast, the subchannel was set to standard resolution (720 x 480 pixels). This corresponds to the resolution before Hi-Vision, and although it is numerically equivalent to DVD, it can be considered that the image quality is slightly lower than DVD because the video format and digital encoding process are different.

If you are watching on a large TV of 50 inches or more, you will feel that the difference in resolution is large.

The sub-channel function has a history of more than 20 years and has been used in Japanese digital broadcasting since the start of BS digital broadcasting. has not been utilized.

While NHK used this feature relatively often, it may not have been familiar to the general public. Regarding the use of sub-channels at the Tokyo Olympics, at first there was only announcements, but perhaps because there were many inquiries, when the live broadcast switched to sub-channels, they actively provided guidance on how to switch channels and how to watch. It is designed to