# Configure time-shifted viewing for MediaTailor channel assembly
<a name="channel-assembly-cdn-timeshift"></a>

AWS Elemental MediaTailor channel assembly supports time-shifted viewing capabilities that enable DVR-like functionality such as pause, rewind, and start-over for your linear channels. Enable these features by configuring your content delivery network (CDN) to support time-shifted viewing, which allows viewers to control their viewing experience.

## Understanding time-shifted viewing
<a name="channel-assembly-cdn-timeshift-overview"></a>

Time-shifted viewing enables DVR-like functionality for linear channels, including:
+ **Start-over**: Viewers can start watching a program from the beginning, even if they join after it has started
+ **Pause and resume**: Viewers can pause content and resume watching later
+ **Rewind and fast-forward**: Viewers can navigate backward and forward through available content
+ **Delayed viewing**: Viewers can watch content that aired earlier in the channel's schedule

Time-shifted viewing works by adding a `start` parameter to the channel's playback URL. The parameter specifies an offset in seconds relative to the current time:
+ Negative values indicate a time in the past (such as `start=-3600` means "start from 1 hour ago")
+ Positive values indicate a time in the future (such as `start=3600` means "start from 1 hour in the future")

Example URL with time-shift parameter:

```
https://example-cdn.com/out/v1/channel-name/index.m3u8?start=-3600
```

## Time delay resolution
<a name="channel-assembly-cdn-timeshift-delay"></a>

To support time-shifted viewing with a CDN:

1. Configure your CDN to forward the `start` query parameter to channel assembly.

1. Set up cache behaviors that include the `start` parameter in the cache key.

1. For manifests with time-shift parameters, use a short TTL or no caching.

This ensures that each viewer receives the correct manifest for their requested time position.

## CDN requirements for time-shifting
<a name="channel-assembly-cdn-timeshift-requirements"></a>

Your CDN must meet these requirements to support time-shifted viewing with channel assembly:
+ Forward all query parameters to channel assembly.
+ Include the `start` parameter in the cache key.
+ Support proper cache invalidation for time-shifted manifests.
+ Handle varying manifest responses based on query parameters.