[wp-trac] [WordPress Trac] #64876: Media: add filter on client-side supported MIME types

[WordPress Trac]

#64876: Media: add filter on client-side supported MIME types
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 Reporter:  adamsilverstein  |      Owner:  (none)
     Type:  enhancement      |     Status:  new
 Priority:  normal           |  Milestone:  7.1
Component:  Media            |    Version:  trunk
 Severity:  normal           |   Keywords:
  Focuses:                   |
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 == Description

 Currently, the list of MIME types supported by client-side media
 processing (via WebAssembly-based vips) is hardcoded. This makes it
 impossible for plugins to add support for additional formats or restrict
 processing to a subset of formats.

 This ticket adds a `client_side_supported_mime_types` filter that allows
 plugins to customize which image formats are processed client-side. The
 filtered list is exposed via the REST API root index endpoint (for users
 with the `upload_files` capability) and consumed by the JavaScript upload
 media store.

 === Changes

 **REST API (class-wp-rest-server.php)**
 - Add `client_side_supported_mime_types` field to the REST API root index
 response
 - Add `client_side_supported_mime_types` filter with default value:
 `['image/jpeg', 'image/png', 'image/gif', 'image/webp', 'image/avif']`
 - Only exposed when `current_user_can( 'upload_files' )`

 **Preload paths (edit-form-blocks.php, site-editor.php)**
 - Add `client_side_supported_mime_types` to the preloaded root fields list
 in both the post editor and site editor
 - Required so the preloaded URL matches the JavaScript request, avoiding
 an extra fetch on editor load

 === Example usage

 ```php
 // Remove AVIF from client-side processing.
 add_filter( 'client_side_supported_mime_types', function ( $mime_types ) {
     return array_diff( $mime_types, array( 'image/avif' ) );
 } );
 ```

 ```php
 // Add HEIC to client-side processing.
 add_filter( 'client_side_supported_mime_types', function ( $mime_types ) {
     $mime_types[] = 'image/heic';
     return $mime_types;
 } );
 ```

 == Props

 adamsilverstein

 == Related

 - Gutenberg PR: https://github.com/WordPress/gutenberg/pull/76549
 - Core PR: https://github.com/WordPress/wordpress-develop/pull/11277

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Ticket URL: <https://core.trac.wordpress.org/ticket/64876>
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