fix(previews): Allow to parse big files for previews

Signed-off-by: Git'Fellow <12234510+solracsf@users.noreply.github.com>

Author: solracsf

config/config.sample.php

@@ -2320,6 +2320,18 @@
  */
 'files_external_allow_create_new_local' => true,
 
+/**
+ * Controls whether to attempt downloading the entire file for preview generation
+ * on non-local storage (e.g., S3, WebDAV) when the initial 5 MB chunk fails to provide
+ * sufficient data for a preview. By default, only the first 5 MB of a file is parsed.
+ *
+ * Enabling this option may significantly increase bandwidth usage and processing time
+ * for large files on external storages.
+ *
+ * * Defaults to ``false``
+ */
+'files_external_full_previews' => false,
+
 /**
  * Specifies how often the local filesystem (the Nextcloud data/ directory, and
  * NFS mounts in data/) is checked for changes made outside Nextcloud. This

lib/private/Preview/Movie.php

@@ -18,7 +18,6 @@
 
 class Movie extends ProviderV2 {
 	private IConfig $config;
-
 	private ?string $binary = null;
 
 	public function __construct(array $options = []) {
@@ -57,11 +56,10 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 			// Try downloading 5 MB first, as it's likely that the first frames are present there.
 			// In some cases this doesn't work, for example when the moov atom is at the
 			// end of the file, so if it fails we fall back to getting the full file.
-			// Unless the file is not local (e.g. S3) as we do not want to download the whole (e.g. 37Gb) file
-			if ($file->getStorage()->isLocal()) {
-				$sizeAttempts = [5242880, null];
-			} else {
-				$sizeAttempts = [5242880];
+			$sizeAttempts = [5242880];
+			$fullPreviews = $this->config->getSystemValueBool('files_external_full_previews', false);
+			if ($file->getStorage()->isLocal() || $fullPreviews === true) {
+				$sizeAttempts[] = null;
 			}
 		} else {
 			// size is irrelevant, only attempt once