Merge pull request #61183 from nextcloud/backport/60916/stable33

[stable33] fix(previews): ffprobe hangs

Author: artonge

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>

lib/private/Preview/Movie.php

@@ -285,8 +285,10 @@ 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');
@@ -337,6 +339,8 @@ 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);