[FFmpeg-devel] [PATCH] avformat/mov: Merge tts after building index for old-style uncomrpessed PCM (PR #20578)

[Derek Buitenhuis via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #20578 opened by Derek Buitenhuis (dwbuiten)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20578
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20578.patch

This was a regression introduced in 292c1df7c159c8a1a7afe52613d164ff417e81ce.

Since we don't know the length of the stts data until after building the
index, since we're generating it, we need to merge any ctts data after,
since otherwise tts_count is set to 0, and no packets will be output.

We can't remove the merge entirely, because uncompressed PCM with
a ctts atom is technically valid (e.g. a constant CTS offset).

This fixes old-style uncompressed PCM demuxing.


>From 605603fb243229c41d3994ae500fde58cce037f0 Mon Sep 17 00:00:00 2001
From: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Date: Mon, 22 Sep 2025 20:00:54 +0100
Subject: [PATCH] avformat/mov: Merge tts after building index for old-style
 uncomrpessed PCM

This was a regression introduced in 292c1df7c159c8a1a7afe52613d164ff417e81ce.

Since we don't know the length of the stts data until after building the
index, since we're generating it, we need to merge any ctts data after,
since otherwise tts_count is set to 0, and no packets will be output.

We can't remove the merge entirely, because uncompressed PCM with
a ctts atom is technically valid (e.g. a constant CTS offset).

This fixes old-style uncompressed PCM demuxing.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
---
 libavformat/mov.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 216c6a5442..7fe4678234 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -4841,10 +4841,6 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
         if (!sc->chunk_count || sc->tts_count)
             return;
 
-        ret = mov_merge_tts_data(mov, st, MOV_MERGE_CTTS);
-        if (ret < 0)
-            return;
-
         // compute total chunk count
         for (i = 0; i < sc->stsc_count; i++) {
             unsigned count, chunk_count;
@@ -4939,6 +4935,10 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
                 chunk_samples -= samples;
             }
         }
+
+        ret = mov_merge_tts_data(mov, st, MOV_MERGE_CTTS);
+        if (ret < 0)
+            return;
     }
 
     if (!mov->ignore_editlist && mov->advanced_editlist) {
-- 
2.49.1

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