> ## Documentation Index > Fetch the complete documentation index at: https://developers.telnyx.com/llms.txt > Use this file to discover all available pages before exploring further. # Modifying MMS SMIL Template > Customize the SMIL template used by Telnyx MMS to control how images, video, and text are laid out and rendered on recipient devices for picture messages. SMIL specifies how MMS media files are laid out in MMS. Telnyx generates SMIL automatically based on `media_urls` and `text` fields. Advanced users can add a `smil_template` parameter to the MMS message request. This template will then be used to generate a customized SMIL. Example of SMIL template: ```xml theme={null}

``` Note that the template has parameters enclosed in double braces `{{ }}`. During the construction of SMIL these parameters will be automatically replaced with locations of text and media contents. In case of media, `{{ 0 }}` will be replaced with the location of the first URL in the `media_urls` list, `{{ 1 }}` will be replaced with the location of the second URL in the `media_urls` list, and so on. `{{ text }}` will be replaced with the location of the `text` content. The SMIL template must be set in `smil_template` parameter of the MMS request. It must be properly JSON-escaped: ```json theme={null} { "from": "+13125551234", "to": "+18655551234", "text": "Hello from Telnyx", "media_urls": ["https://example.com/media.jpg"], "smil_template": "\n\t\n\t\t