PDF thumbnails to WEBP/AVIF

[1ucay]

Dear all,

if you upload PDF, in metadata sizes we have array with jpgs.

I tried fix with

add_filter( 'webp_uploads_upload_image_mime_transforms', 'core_webp_uploads_upload_image_mime_transforms', 9, 2 );
function core_webp_uploads_upload_image_mime_transforms( $default_transforms ) {

    $mimes = wp_get_mime_types();

    $output_format = webp_uploads_mime_type_supported( 'image/avif' ) ? webp_uploads_get_image_output_format() : 'webp';
    $transforms    = webp_uploads_is_fallback_enabled() ? array( 'image/jpeg', 'image/' . $output_format ) : array( 'image/' . $output_format );

    foreach( $mimes as $k => $v ) {
        if ( ! isset( $default_transforms[ $v ] ) )
            $default_transforms[ $v ] = $transforms;
    }

    return $default_transforms;
}

If you upload PSD with mime image/vnd.adobe.photoshop and genereate sizes with some custom code (imagemagick support PSD) like PDF does

add_filter( 'wp_generate_attachment_metadata', 'core_wp_generate_attachment_metadata', 9, 2 );

it working ok. I have nice jpg and avif in metadata.

But, different situation is with PDF mime application/pdf. It is blocked by helper.php line 145

$image_path = wp_get_original_image_path( $attachment_id );

and inside function is condition

  if ( ! wp_attachment_is_image( $attachment_id ) ) {

We dont have any filter skip this check, so PDF avif is not working. Best would be add filter to "wp_attachment_is" and override.

Im working on LibreOffice (exec soffice), audiowave (exec https://github.com/bbc/audiowaveform ) , PSD / AI (imagemagick) thumbnailer.
https://core.trac.wordpress.org/ticket/62712

[AhmarZaidi]

Hey @1ucay

If I understand correctly, the issue is that PDF uploads should generate previews, but generation is blocked because wp_get_original_image_path() checks wp_attachment_is_image(), which returns false for PDFs.

I did try to replicate the issue and did not get pdf previews but I was unable to confirm if that is due to ! wp_attachment_is_image( $attachment_id ).

If you could revisit the issue once more and provide replication instructions, it would be very helpful.

[1ucay]

Dear @AhmarZaidi
yes, exactly, for AVIF previews it is blocked by wp_attachment_is_image, if mime type of file is not image/
Would be possible add some apply_filters?

[1ucay]

you can add application/pdf over webp_uploads_upload_image_mime_transforms

[AhmarZaidi]

@1ucay Thanks for the confirmation.

There already exist a filter webp_uploads_upload_image_mime_transforms which we can use to add application/pdf mimetype to transforms like so:

add_filter( 'webp_uploads_upload_image_mime_transforms', function( $transforms ) {
    $transforms['application/pdf'] = array( 'image/jpeg' );
    return $transforms;
});

A possible solution could be to add application/pdf mimetype to the default list and use get_attached_file() function for getting the original pdf file path if mime type is application/pdf to bypass $image_path = wp_get_original_image_path( $attachment_id );

---

Now, it doesn't work when I have the dev environment running using npm run wp-env start and shows security policy error:

WP_Error Object
(
    [errors] => Array
    (
        [invalid_image] => Array
        (
            [0] => attempt to perform an operation not allowed by the security policy `PDF' @ error/constitute.c/IsCoderAuthorized/426
        )
    )

    [error_data] => Array
    (
        [invalid_image] => /var/www/html/wp-content/uploads/2025/02/test.pdf
    )

    [additional_data:protected] => Array ()
)

This appears to be an issue with ImageMagick policy used in the docker WordPress environment. Solutions suggest changing the ImageMagick policy

---

However, looking into the core file reveal that it should work so I tested the solution on other setups like localWP (by separately adding Modern Image Formats plugin) and it seems to work fine.

Screen.Recording.2025-02-12.at.8.48.56.AM.mov

Feel free to let me know if I've understood or implemented something incorrectly.

[1ucay]

I have some workaround for this. but it so hacky ;) I can upload even PSD file (image/vnd.adobe.photoshop), which is by ImageMagick supported format. It will create thumbnail sizes (jpg,avif), I can even work in WP image editor (cropping etc). But it will be separate plugin.

Best solution for every usecase would be add filter to wp_attachment_is_image. So user can override function.

You have to change post_mime_type in WP Post object after filter "webp_uploads_pre_generate_additional_image_source"

<?php

if ( ! defined( 'ABSPATH' ) ) {
    die( 'Cannot access pages directly.' );
}

function core_get_image_viewable_formats() {
    return array( 'image/jpeg', 'image/png', 'image/apng', 'image/gif', 'image/bmp', 'image/webp', 'image/avif' );
}

// important hook with priority 10!! otherwise not working second image edit
add_filter( 'wp_update_attachment_metadata', 'core_thumbnail_generator_wp_update_attachment_metadata', 10, 2 );
function core_thumbnail_generator_wp_update_attachment_metadata( $meta, $attachment_id ) {

    if ( ! did_action( 'core_thumbnail_generator_alter_post_mime_type' ) )
        return $meta;

    $old_meta = wp_get_attachment_metadata( $attachment_id );

    $meta['sizes']['full'] = array(
        'file'      => wp_basename( apply_filters( 'image_make_intermediate_size', $meta['file'] ) ),
        'width'     => $meta['width'],
        'height'    => $meta['height'],
        'mime-type' => $meta['sizes']['full']['mime-type'],
        'filesize'  => $meta['filesize']
    );

    $meta['width']    = $old_meta['width'];
    $meta['height']   = $old_meta['height'];
    $meta['filesize'] = $old_meta['filesize'];

    return $meta;
}

// fix for AVIF / WEBP for Modern Image Formats
add_filter( 'webp_uploads_upload_image_mime_transforms', function( $transforms ) {
    $transforms['application/pdf'] = array( 'image/jpeg' );
    return $transforms;
});

add_filter( 'webp_uploads_pre_generate_additional_image_source', 'core_thumbnail_generator_webp_uploads_pre_generate_additional_image_source', 10, 5 );
function core_thumbnail_generator_webp_uploads_pre_generate_additional_image_source( $return, $attachment_id, $image_size, $size_data, $mime ) {

    core_thumbnail_generator_alter_post_mime_type( $attachment_id, false );

    return;
}

add_filter( 'wp_update_attachment_metadata', 'core_thumbnail_generator_wp_update_attachment_metadata_webp', 11, 2 );
function core_thumbnail_generator_wp_update_attachment_metadata_webp( $meta, $attachment_id ) {

    if ( did_filter( 'webp_uploads_upload_image_mime_transforms' ) && isset( $meta['sources'] ) && isset( $meta['sizes'] ) && isset( $meta['sizes']['full'] ) ) {

        // revert alter mime
        $attachment = wp_cache_get( $attachment_id, 'posts' );

        if ( isset( $attachment->post_mime_type_backup ) ) {

            $attachment->post_mime_type = $attachment->post_mime_type_backup;
            unset( $attachment->post_mime_type_backup );
            wp_cache_set( $attachment->ID, $attachment, 'posts' );

            if ( isset( $meta['sources'][ $attachment->post_mime_type ] ) ) {

                unset( $meta['sources'][ $attachment->post_mime_type ] );

                $meta['sources'][ $meta['sizes']['full']['mime-type'] ] = array(
                    'file'     => $meta['sizes']['full']['file'],
                    'filesize' => $meta['sizes']['full']['filesize'],
                );

            }

            remove_filter( 'get_attached_file', 'core_thumbnail_generator_get_attached_file', 10, 2 );

        }
    }

    return $meta;
}

function core_thumbnail_generator_update_attached_file( $file, $attachment_id ) {

    add_filter( 'update_post_metadata', function( $return, $object_id, $meta_key, $meta_value, $prev_value ) {

        remove_filter( current_filter(), __FUNCTION__ );

        if ( '_wp_attached_file' === $meta_key )
            return true;

    }, 10, 5 );

    return get_post_meta( $attachment_id, '_wp_attached_file', true );

}

function core_thumbnail_generator_alter_post_mime_type( $attachment_id = null ) {

    $post = get_post( $attachment_id );

    $attachment = wp_cache_get( $attachment_id, 'posts' );

    if ( ! $attachment || is_a( $attachment, 'WP_Post' ) )
        return;

    if ( in_array( $attachment->post_mime_type, core_get_image_viewable_formats() ) )
        return;

    $sizes = image_get_intermediate_size( $attachment->ID, 'full' );
    if ( ! $sizes )
        return;

    $attachment->post_mime_type_backup = $attachment->post_mime_type;
    $attachment->post_mime_type = $sizes['mime-type'];

    wp_cache_set( $attachment->ID, $attachment, 'posts' );

    add_filter( 'get_attached_file', 'core_thumbnail_generator_get_attached_file', 10, 2 );
    
    do_action( 'core_thumbnail_generator_alter_post_mime_type' );
}

function core_thumbnail_generator_get_attached_file( $filepath, $attachment_id ) {

    if ( $full_size = image_get_intermediate_size( $attachment_id, 'full' ) )
        $filepath = path_join( dirname( $filepath ), $full_size['file'] );

    return $filepath;
}


// bug wordpress-develop/src/wp-includes/media.php @4613, psd is image, but cannot be editable
add_filter( 'wp_prepare_attachment_for_js', 'core_thumbnail_generator_wp_prepare_attachment_for_js', 10, 3 );
function core_thumbnail_generator_wp_prepare_attachment_for_js( $response, $attachment, $meta ) {

    if ( ! empty( $meta['sizes'] ) && ( isset( $attachment->post_mime_type_backup ) || ! in_array( $attachment->post_mime_type, core_get_image_viewable_formats() ) ) ) {

        $attachment_url = wp_get_attachment_url( $attachment->ID );
        $base_url       = str_replace( wp_basename( $attachment_url ), '', $attachment_url );

        if ( $full_size = image_get_intermediate_size( $attachment->ID, 'full' ) ) {
            $response['sizes']['full'] = array(
                'url'         => $base_url . $full_size['file'] . ( str_contains( wp_get_referer(), '&mode=edit' ) ? '?' . time() . rand( 100, 999 ) : '' ),
                'height'      => $full_size['height'],
                'width'       => $full_size['width'],
                'orientation' => $full_size['height'] > $full_size['width'] ? 'portrait' : 'landscape',
            );
            $response['editable'] = true;
            return $response;
        }
    }


    return $response;
}

[AhmarZaidi]

I've created a draft PR with the previous approach before noticing there's an update 😅:

A possible solution could be to add application/pdf mimetype to the default list and use get_attached_file() function for getting the original pdf file path if mime type is application/pdf to bypass $image_path = wp_get_original_image_path( $attachment_id );

Will be reviewing and testing the new approach:

Best solution for every usecase would be add filter to wp_attachment_is_image. So user can override function.

[1ucay]

Nice, thank you, but it is solution only for PDF :)
What about, if I have thumbnail for different type of document, for example docx, waveform of mp3 etc?

My proposal

$image_path = in_array( get_post_mime_type( $attachment_id ), array( 'image/jpeg', 'image/webp', 'image/avif', 'image/png' ) ) ? wp_get_original_image_path( $attachment_id ) : get_attached_file( $attachment_id );