Time representation for use with media containers.
A MediaTime can be thought of as "sample #count at rate Hz".
This representation is precise, even for large values, because the sample count and rate are stored separately and do not make use of floating point storage.
| Invalid | Invalid time value. |
| count | The sample count for the time value. |
| rate | The rate used for converting the count into seconds. |
| MediaTime | Creates a time value with an integer number of seconds, using 1Hz for the rate. |
| Unknown operator | Returns the time value expressed as a floating point number of seconds. |