# Time-shifting a channel's playback
<a name="channel-assembly-time-shift"></a>

With MediaTailor channel assembly, you can time-shift a channel's playback. Time-shifting allows viewers to watch a channel's content at a time other than the original broadcast time. For example, a viewer can start watching a program from the beginning, even if they join the broadcast after it has started. Or, a viewer can pause a program and resume watching it later.

To time-shift a channel's playback, you add a `start` parameter to the channel's playback URL. The `start` parameter specifies the time when playback should begin, relative to the current time. For example, if the current time is 2:00 PM, and you want to start playback from 1:00 PM, you would set the `start` parameter to `-3600`, which is -1 hour in seconds.

The `start` parameter accepts both positive and negative values, in seconds:
+ Negative values indicate a time in the past, relative to the current time. For example, `start=-3600` means "start playback from 1 hour ago."
+ Positive values indicate a time in the future, relative to the current time. For example, `start=3600` means "start playback from 1 hour in the future."

The following example shows how to add the `start` parameter to a channel's playback URL:

```
https://a1b2c3d4e5f6.mediapackage.us-west-2.amazonaws.com/out/v1/examplechannel/index.m3u8?start=-3600
```

In this example, playback starts from 1 hour ago.

The `start` parameter is subject to the following limitations:
+ The maximum time-shift window is 24 hours in the past or future.
+ Time-shifting is only available for channels that use the linear playback mode.
+ Time-shifting is not available for channels that use the loop playback mode.

If you specify a `start` parameter that is outside the available time-shift window, MediaTailor returns an error.