When a course is setup it has an associated distance (e.g. so many laps, a GPS trace of a certain length), and sometimes an associated time (e.g. 20 minutes of laps or a GPS trace that took 30 minutes that particular time).
Usually you would want to ride by distance, so your 10 mile ride is 10 miles, and if you ride it quick or slow it takes the relevant amount of time. This is how most "courses" would likely be done.
If a video is associated with a route done by distance, the video will speed up and slow down to match the speed you are cycling, and will get to the end the same time you do.
However, sometimes you would rather cycle for a specified time, no matter how much or little distance is covered, for example if you are doing interval training or some other pre-defined exercise such as pedal flat out for 5 minutes, then rest for 20 minutes, then repeat. For example, you can create manual sessions by time, with a specified amount of time at a specified gradient, very useful for interval training.
So if you want to ride "intervals" like this, you can choose to ride by time, and it is a case of how much distance can you cover in the prescribed time (e.g. how many laps of the velodrome in 20 minutes).
If a video is associated with a route done by time, it will not speed up or slow down to match you, it will just play for the specified time, and you may cover more or less than the mileage originally associated with the session. Therefore the video will not be synched to your riding, or represent where you are on the course (you may be far past the end of the video).
Generally schedule "Routes" by distance (especially with video), and "Intervals" or interval training by time.
One word of warning, if you do a session by time, you cannot export it to a .fit file for importing into Strava, etc. It gives a message that "interval sessions" cannot currently be exported.
Cheers,
Geoff
5300 ft of it
