# Updating SMIL playlist - PULL mode ## Updating the Players To supply fresh content to a player, one must specify the `Refresh` meta attribute in the first SMIL playlist loaded from the server. The syntax is as follows: ```xml ``` The SMIL player reaches the SMIL playlist URL and checks the Last-modified header. Once a new version of the playlist is uploaded, it is recognized, downloaded, and played. ### Update Check Intervals The SMIL Player supports separate update intervals for media files and the SMIL file itself: ```xml ``` - `content` - defines the check interval for media files in seconds; for backward compatibility, if used alone, applies to media files. - `contentRefresh` - explicitly sets the check interval for media files in seconds; use when you want separate intervals. - `smilFileRefresh` - sets the check interval for the SMIL file in seconds (default: 86400 seconds/24 hours). - `expr` - limits the check interval based on [expression](https://docs.signageos.io/hc/en-us/articles/4405241217810); optional. - `timeOut` - sets the timeout for HEAD requests in milliseconds (default: 2000ms); optional. Useful for slower or unstable networks where you may want to increase the timeout (e.g., 5000-10000ms). - `skipContentOnHttpStatus` - automatically skip media files that return specified HTTP error codes (e.g., "404" or "403,404,500"); optional. This prevents playback interruption when content is unavailable. - `updateContentOnHttpStatus` - force re-download of media files that return specified HTTP status codes (e.g., "200,205"); optional. This works alongside last-modified headers as an additional update trigger mechanism. - `fallbackToPreviousPlaylist` - when set to true, continues playing the current playlist if an invalid SMIL file is provided during an update (default: false); optional. Prevents disruption from deployment errors. - `onlySmilUpdate` - when set to true, the player only checks the actual SMIL file for updates and not the media specified within the SMIL file. By using `expr`, you can limit the time when the signageOS SMIL Player checks for an update during a selected time period, e.g., from 1 am to 6 am: `expr="compare(time(),'01:00:00')>0 and compare(time(), '6:00:00')<0"` ### Benefits of Separate Update Intervals Splitting media and SMIL file checks provides several advantages: 1. **Performance Optimization**: Reduce unnecessary HEAD requests for stable SMIL files while keeping media content fresh 2. **Bandwidth Efficiency**: SMIL files typically change less frequently than media content 3. **Flexible Update Strategies**: - Dynamic content (news, weather) can update frequently - Playlist structure can remain stable with less frequent checks 4. **Backward Compatibility**: Using only `content` attribute continues to work for media file checks **Common Use Cases:** - **Dynamic Content Feeds**: Check media every 30 seconds, SMIL daily - **Stable Playlists**: Check media hourly, SMIL weekly - **Live Events**: Frequent media updates during events, rare SMIL changes ### Examples with Different Configurations ```xml ``` ### Content Error Handling When `skipContentOnHttpStatus` is configured: - Media files returning the specified HTTP status codes are automatically skipped - The playlist continues playing the next available content - This prevents black screens or playback interruption when content is temporarily or permanently unavailable - Common use cases include: - Dynamic content that may not always be available (404 - Not Found) - Access-restricted content (403 - Forbidden) - Server errors (500 - Internal Server Error, 503 - Service Unavailable) ### Forced Content Updates The `updateContentOnHttpStatus` attribute provides an additional update mechanism alongside last-modified headers: ```xml ``` How it works: - When HEAD request returns a configured status code, the content is marked for re-download - This works **in addition to** last-modified header checks - Useful when servers use status codes to signal content updates - The player will re-download the content even if last-modified hasn't changed Common use cases: - **HTTP 200**: Force refresh of dynamic content on successful response - **HTTP 205 (Reset Content)**: Server explicitly requests content refresh - **Custom CDN codes**: Some CDNs use specific codes to signal new versions - **Dynamic content APIs**: Services that signal updates through status codes This provides flexibility for servers that: - Don't properly set last-modified headers - Use status codes as update signals - Need to force updates regardless of timestamps ### Fallback to Previous Playlist The `fallbackToPreviousPlaylist` attribute provides protection against invalid SMIL updates: ```xml ``` When enabled: - If an invalid or broken SMIL file is deployed, the player continues with the current valid playlist - No backup image is shown - the display continues uninterrupted - The player keeps checking for valid updates in the background - Once a valid SMIL is found, it will be loaded and played This is particularly useful for: - Production environments where display continuity is critical - Preventing accidental deployment of broken configurations - Maintaining playback during CMS or server issues - Avoiding the backup image display for temporary problems **Note:** Without this option, an invalid SMIL update would trigger the backup image display. > ### Important: HEAD requests >The SMIL player makes a `HEAD` request to check `Last-modified` instead of using GET/POST. This method saves bandwidth. > > If you encounter CORS issues, ensure that your CDN/storage supports CORS for `HEAD` requests as well. If the `Refresh` information is missing, a default value of (`20` seconds) is used. Source: [a-smil.org](https://www.a-smil.org/index.php/Main_Page)