From 136b88180b78f6894b996d3cad2a9d8f18fa3ad1 Mon Sep 17 00:00:00 2001
From: Andrey Dyakov <adduxa@gmail.com>
Date: Fri, 5 Jun 2026 00:03:11 +0400
Subject: [PATCH] fix(previews): ffprobe hangs

Signed-off-by: Andrey Dyakov <adduxa@gmail.com>
---
 AUTHORS                       | 1 +
 lib/private/Preview/Movie.php | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/AUTHORS b/AUTHORS
index fe478401fddb4..fa5776e3ef575 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 f34bf60c14773..334de993deaa9 100644
--- a/lib/private/Preview/Movie.php
+++ b/lib/private/Preview/Movie.php
@@ -289,8 +289,10 @@ 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');
@@ -341,6 +343,8 @@ 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);