ATSC M/H Slot [EtherGuide Glossary]
An ATSC M/H Slot is the basic conceptual element employed in allocating 8-VSB transport packets between main (MPEG-2) service and M/H service. Each M/H slot is 156 bytes (29,328 bits)in length and encompasses around 12.1 ms of time. There are 4 M/H slots in each 8-VSB data frame.
The table below shows how the data within an individual ATSC M/H slot can be allocated between main and M/H service.
| contents | main service | M/H service |
| packets | bits | packets | bits |
| MPEG-2 only | 156 | 29,328 | 0 | 0 |
| mixed | 38 | 7,144 | 118 | 22,184 |
Whether a particular M/H slot contains all MPEG-2 packets or mostly M/H data and a few MPEG-2 packets is determined dynamically by the instantaneous needs of the main (MPEG-2)and ATSC M/H encoders and the various other units in the processing chain.
Each 8-VSB data frame spans 624 MPEG-2 packets (938,496 bits). In ATSC M/H usage, each 8-VSB data frame can contain either 72 MPEG-2 packets (108,288 bits) and 138 ATSC M/H packets (830,208) or, if no ATSC M/H data is present in a data frame, 624 MPEG-2 packets
Glossary
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