PR #24779 opened by ffmpeg-devel
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24779
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24779.patch

**Backport:** https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24665

So far, if an avformats write_trailer call returned a positive value instead of 
0, like for example movenc does for the number of bytes written, it would hide 
any pb context failures.
This adjusts the check to expect positive return values, and only overwrites 
them with the pb error if it actually had an error, to preserve the return 
value in case something came to rely on it.


>From 85b823bb6b6cb685c6d8f2797b456a38a5631cce Mon Sep 17 00:00:00 2001
From: Timo Rothenpieler <[email protected]>
Date: Thu, 24 Sep 2026 14:21:41 +0200
Subject: [PATCH] avformat/mux: don't let positive write_trailer ret shadow pb
 failure

(cherry picked from commit 1de217ad4b98163b7f5a372853b1c943ed6f070d)
---
 libavformat/avformat.h | 2 +-
 libavformat/mux.c      | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index f12fa7d904..0ebfc6ebdd 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -2471,7 +2471,7 @@ int av_write_uncoded_frame_query(AVFormatContext *s, int 
stream_index);
  * May only be called after a successful call to avformat_write_header.
  *
  * @param s media file handle
- * @return 0 if OK, AVERROR_xxx on error
+ * @return >=0 if OK, AVERROR_xxx on error
  */
 int av_write_trailer(AVFormatContext *s);
 
diff --git a/libavformat/mux.c b/libavformat/mux.c
index 31361f9b46..73ac317073 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -1282,8 +1282,8 @@ int av_write_trailer(AVFormatContext *s)
 
     if (s->pb)
        avio_flush(s->pb);
-    if (ret == 0)
-       ret = s->pb ? s->pb->error : 0;
+    if (ret >= 0 && s->pb && s->pb->error < 0)
+       ret = s->pb->error;
     for (unsigned i = 0; i < s->nb_streams; i++) {
         av_freep(&s->streams[i]->priv_data);
         av_freep(&ffstream(s->streams[i])->index_entries);
-- 
2.52.0

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