can you explain me how to obtain Duration and length of a media file?

ah, I'm on drupal11

ok, I write this for people that could have same problem.
The solution that I have found is to write a custom module.
Ok, Deepseek writes it for me, I adjust it and you can use this solution and works:

1.
First of all create 2 field in your content type, filesize and duration, they should be numbers.

2. The module require getid3, so:

composer require james-heinrich/getid3

3. Create a subdirectory into modules/custom and call it for example audiometadatahelper.
Put there 2 files, audiometadatahelper.info.yml and audiometadatahelper.module.

4.
Content of audiometadatahelper.info

name: audioMetadata Helper
description: 'provides the values of size and duration and writes them in the fields'
type: module
core_version_requirement: ^11
package: Custom

5. Content of audiometadatahelper.module

<?php

use Drupal\Core\Entity\EntityInterface;
use Drupal\media\MediaInterface;
use Drupal\file\FileInterface;

/**
 * Implements hook_entity_presave().
 */
function audiometadatahelper_entity_presave(EntityInterface $entity) {
  // Verify it is a podcast content type
  if ($entity->getEntityTypeId() === 'node' && $entity->bundle() === 'podcast') {
    // Load media audio (field_file_audio) field
    if ($entity->hasField('field_file_audio') && !$entity->get('field_file_audio')->isEmpty()) {
      $media_entity = $entity->get('field_file_audio')->entity;
      
      if ($media_entity instanceof MediaInterface) {
        // File field in the media Type(modify if necessary)
        $media_file_field = 'field_media_audio_file';
        if ($media_entity->hasField($media_file_field)) {
          $audio_file = $media_entity->get($media_file_field)->entity;
          
          if ($audio_file instanceof FileInterface) {
            // 1. Save the file size
            if ($entity->hasField('field_filesize')) {
              $entity->set('field_filesize', $audio_file->getSize());
            }
            
            // 2. Calculate and save the duration
            if ($entity->hasField('field_duration')) {
              $uri = $audio_file->getFileUri();
              $duration = audiometadatahelper_get_audio_duration($uri);
              $entity->set('field_duration', $duration);
            }
          }
        }
      }
    }
  }
}

/**
 * Extract the duration of audio using Getid3.
 */
function audiometadatahelper_get_audio_duration($uri) {
  $realpath = \Drupal::service('file_system')->realpath($uri);
  
  if (class_exists('getID3')) {
    $getID3 = new getID3();
    try {
      $file_info = $getID3->analyze($realpath);
      return $file_info['playtime_seconds'] ?? 0;
    } catch (\Exception $e) {
      \Drupal::logger('audiometadatahelper')->error('Errore analisi audio: @error', ['@error' => $e->getMessage()]);
    }
  }
  
  return 0;
}

6. Install the module and enjoy! When you upload a file and save the content, filesize and duration will be populated, so you can map them from the podcast module.

Finally, I want to clarify that I am absolutely not a programmer. I just found a solution that works for me.
Maybe I hope to help others and save their hours of study.