External media support

The Sinch platform supports playing audio files during a call. Audio files can be provided through a public URL, and multiple audio formats are supported.

External media is accessed by providing a valid URL in the play.url property of a PLAY message within the SVAML messages command. Supported URL schemes are HTTP and HTTPS. The URL must point directly to the media file; redirects are not supported.

When a media file is downloaded for the first time, playback can be delayed. Delay depends on file size and the source server's upload speed.

After a successful download, the platform stores a local copy of the media file. This reduces repeated traffic between Sinch and the partner backend and helps reduce playback latency.

The following caching rules apply:

When a Cache-Control header is present:

• The platform uses the max-age directive to determine cache duration.
• The minimum supported duration is 24 hours; values below 24 hours are treated as 24 hours.
• This duration is absolute and expires exactly after the specified time from the moment the file was downloaded.

When no Cache-Control header is present:

• The file is cached for 24 hours from the last access time.
• Expiration is extended by 24 hours each time the media resource is used.

Consider the following limits when providing an external media reference:

• File size is limited to 1 MB by default.
• Download attempts are limited to 50 per hour.
• Total downloaded content is limited to 50 MB per hour.

For larger files or a higher hourly content limit, contact Sinch support.

When accessing an external media resource, the platform requires a Content-Type header in the response. The following values are supported: