[FFmpeg-devel] [PATCH] avformat/movenc: clear subsample information on fragment flush (PR #20538)

[James Almer via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #20538 opened by James Almer (jamrial)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20538
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20538.patch

Don't keep around information from a previous traf atom.

Fixes issue #20492.


>From 9c18a8d1802726c7d59c5d067890b7f2f8c728f4 Mon Sep 17 00:00:00 2001
From: James Almer <jamrial@gmail.com>
Date: Tue, 16 Sep 2025 21:45:00 -0300
Subject: [PATCH] avformat/movenc: clear subsample information on fragment
 flush

Don't keep around information from a previous traf atom.

Fixes issue #20492.

Signed-off-by: James Almer <jamrial@gmail.com>
---
 libavformat/movenc.c     | 3 +++
 libavformat/movenccenc.c | 6 ++++++
 libavformat/movenccenc.h | 6 ++++++
 3 files changed, 15 insertions(+)

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index bfe76a2034..067d38b14b 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -6592,6 +6592,9 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
             mov_write_moof_tag(s->pb, mov, moof_tracks, mdat_size);
             mov->fragments++;
 
+            if (track->cenc.aes_ctr)
+                ff_mov_cenc_flush(&track->cenc);
+
             avio_wb32(s->pb, mdat_size + 8);
             ffio_wfourcc(s->pb, "mdat");
             mdat_start = avio_tell(s->pb);
diff --git a/libavformat/movenccenc.c b/libavformat/movenccenc.c
index 32094ebd7b..e5ae11a9c9 100644
--- a/libavformat/movenccenc.c
+++ b/libavformat/movenccenc.c
@@ -629,6 +629,12 @@ int ff_mov_cenc_init(MOVMuxCencContext* ctx, uint8_t* encryption_key,
     return 0;
 }
 
+void ff_mov_cenc_flush(MOVMuxCencContext* ctx)
+{
+    ctx->auxiliary_info_entries = 0;
+    ctx->auxiliary_info_size    = 0;
+}
+
 void ff_mov_cenc_free(MOVMuxCencContext* ctx)
 {
     av_aes_ctr_free(ctx->aes_ctr);
diff --git a/libavformat/movenccenc.h b/libavformat/movenccenc.h
index 77a0716c81..f03e2fe6aa 100644
--- a/libavformat/movenccenc.h
+++ b/libavformat/movenccenc.h
@@ -91,6 +91,12 @@ int ff_mov_cenc_avc_write_nal_units(AVFormatContext *s, MOVMuxCencContext* ctx,
 
 int ff_mov_cenc_av1_write_obus(AVFormatContext *s, MOVMuxCencContext* ctx,
                                AVIOContext *pb, const AVPacket *pkt);
+
+/**
+ * Clear subsample data. To be called for fragmented output.
+ */
+void ff_mov_cenc_flush(MOVMuxCencContext* ctx);
+
 /**
  * Write the cenc atoms that should reside inside stbl
  */
-- 
2.49.1

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