Check Before Play

What it does

Instead of relying on periodic HEAD-request polling to detect media updates, the player checks each media file for updates immediately before playing it. This ensures content is always fresh at the moment of playback. See the checkBeforePlay reference entry for exactly what it disables and forces internally.

How to enable

Add the checkBeforePlay="true" attribute to the <meta> tag in the SMIL <head>:

<smil>
    <head>
        <meta http-equiv="Refresh" content="60" checkBeforePlay="true"/>
    </head>
    <!-- Additional elements here -->

</smil>

Note

You don't need to also set onlySmilUpdate="true" — checkBeforePlay forces it internally. See the reference entry linked above for what stays on the periodic interval and what doesn't.

Lookahead via checkAheadCount

Without a lookahead, the HEAD check for element N happens right before element N plays — which can visibly delay the transition while the HEAD (and any triggered download) completes. Set checkAheadCount to have the player check the element N positions ahead while the current element is still playing:

<meta http-equiv="Refresh" content="60" checkBeforePlay="true" checkAheadCount="2"/>

See the checkAheadCount reference entry for the wrap-around behavior, recovery re-checks, and worst-case detection latency.

When to use

This option is useful when content freshness at playback time matters more than update latency — for example:

• Playlists with long-duration items where polling might miss a mid-cycle update.
• Infrequent loop cycles where you want to guarantee the latest version plays on the next iteration.
• Scenarios where you want to reduce unnecessary network traffic from polling media files that haven't changed.

Relation to the playCheckUrl playability gate

checkBeforePlay and the per-element playCheckUrl gate are independent request channels (the update check uses HEAD, the gate uses GET) that can be combined freely. The update check (this page) decides whether content changed and rides the checkAheadCount lookahead when configured; the gate decides whether the element plays this pass and always fires inline right before play — it never rides the lookahead, so its answer is always fresh. Neither channel reads the other's status-code list (skipContentOnHttpStatus vs skipPlaybackOnHttpStatus).

Source: a-smil.org