# Store Video in a Rolling Buffer

Media Server can save a copy of the video it ingests to a rolling buffer. A rolling buffer is a fixed amount of storage where the oldest content is discarded to make space for the latest.

Media Server can write video directly into the rolling buffer, producing an evidential copy that has not been modified in any way. You might require an evidential copy for legal reasons. Media Server can also encode video before writing it to the buffer, creating a non-evidential copy that is optimized for storage and playback.

NOTE: Evidential mode is not supported when the source video is in MJPEG format.

A rolling buffer is useful for both broadcast monitoring and surveillance applications. For example, in a surveillance application you could configure the rolling buffer with sufficient storage to contain all the video captured by a camera in the last 7 days. If an event occurs you can play the content from the rolling buffer and view the video around the time of the event. If you needed to document the event, you would have 7 days to extract images and video from the rolling buffer before the video is overwritten.

Rolling buffers are configured in a separate configuration file (not in the Media Server configuration file). The rolling buffer configuration file contains settings such as the paths to the storage locations on disk, and the amount of storage to allocate to each rolling buffer.

You can configure as many rolling buffers as you need. For example, you could choose to save an evidential copy of the ingested video to one rolling buffer and a smaller compressed copy to another. You might also want to set up multiple rolling buffers if you ingest video from separate cameras or channels. For example, if you ingest 12 hours of video from one channel and then 48 hours from another you can use multiple rolling buffers to store the last 12 hours from each channel.

Video is served from the rolling buffer using the HTTP Live Streaming (HLS) protocol. An HLS-compliant media player can request an HLS playlist from Media Server or the MMAP REST endpoint. The playlist points to video segments in the rolling buffer, and these segments are served by an external component such as a Web server or MMAP. Media Server does not include a Web server.

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