diff --git a/AUTHORS b/AUTHORS
index 8881c9ba26a75..951496aa6a907 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -32,6 +32,7 @@
  - Andreas Pflug <dev@admin4.org>
  - Andrew Brown <andrew@casabrown.com>
  - Andrey Borysenko <andrey.borysenko@nextcloud.com>
+ - Andrey Dyakov <adduxa@gmail.com>
  - André Gaul <gaul@web-yard.de>
  - Andy Xheli <axheli@axtsolutions.com>
  - Anna Larch <anna@nextcloud.com>
diff --git a/lib/private/Preview/Movie.php b/lib/private/Preview/Movie.php
index 7b9c7a26f77b1..7a22551d5dafb 100644
--- a/lib/private/Preview/Movie.php
+++ b/lib/private/Preview/Movie.php
@@ -108,8 +108,10 @@ private function useHdr(string $absPath): bool {
 		if ($test_hdr_proc === false) {
 			return false;
 		}
-		$test_hdr_stdout = trim(stream_get_contents($test_hdr_pipes[1]));
+		// Read stderr before stdout: ffprobe's stderr can exceed 64KB (OS pipe buffer) for certain
+		// files, causing a deadlock if stdout is read first. stdout is always a short string.
 		$test_hdr_stderr = trim(stream_get_contents($test_hdr_pipes[2]));
+		$test_hdr_stdout = trim(stream_get_contents($test_hdr_pipes[1]));
 		proc_close($test_hdr_proc);
 		// search build options for libzimg (provides zscale filter)
 		$ffmpeg_libzimg_installed = strpos($test_hdr_stderr, '--enable-libzimg');
@@ -161,6 +163,8 @@ private function generateThumbNail(int $maxX, int $maxY, string $absPath, int $s
 		$returnCode = -1;
 		$output = '';
 		if (is_resource($proc)) {
+			// Read stderr before stdout: ffmpeg's stderr can exceed 64KB (OS pipe buffer) for certain
+			// files, causing a deadlock if stdout is read first. stdout is always empty.
 			$stderr = trim(stream_get_contents($pipes[2]));
 			$stdout = trim(stream_get_contents($pipes[1]));
 			$returnCode = proc_close($proc);