[FFmpeg-devel] [PATCH] avformat/mpegts: Add AVFMT_FLAG_ALLOW_CODEC_CHANGES

[Pavel Koshevoy]

Make midstream AVStream.codecpar updates optional and disabled
by default, so that avformat API clients can enable this feature
explicitly when they add support for midstream codec changes.
---
 doc/APIchanges              | 3 +++
 doc/formats.texi            | 5 +++++
 libavformat/avformat.h      | 2 ++
 libavformat/mpegts.c        | 4 +++-
 libavformat/options_table.h | 1 +
 libavformat/version.h       | 2 +-
 tests/fate/demux.mak        | 2 +-
 7 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index 91710bb27d..43172fbcdd 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2025-03-28
 
 API changes, most recent first:
 
+2025-06-17 - xxxxxxxxxx - lavf 62.2.100 - avformat.h
+  Add AVFMT_FLAG_ALLOW_CODEC_CHANGES flag.
+
 2025-05-21 - xxxxxxxxxx - lavu 60.3.100 - avassert.h
   Add av_unreachable() and av_assume() macros.
 
diff --git a/doc/formats.texi b/doc/formats.texi
index 876a9e92b3..5a0d070247 100644
--- a/doc/formats.texi
+++ b/doc/formats.texi
@@ -39,6 +39,11 @@ Set format flags. Some are implemented for a limited number of formats.
 
 Possible values for input files:
 @table @samp
+ at item allow_codec_changes
+Allow AVStream.codecpar to change midstream if input changes
+(for example when MPEG-TS ES stream_type changes).
+This is disabled by default, because most clients of avformat API
+do not support random midstream codec changes.
 @item discardcorrupt
 Discard corrupted packets.
 @item fastseek
diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index b6c63e2237..2e5232c96d 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -1436,6 +1436,8 @@ typedef struct AVFormatContext {
 #define AVFMT_FLAG_FAST_SEEK   0x80000 ///< Enable fast, but inaccurate seeks for some formats
 #define AVFMT_FLAG_AUTO_BSF   0x200000 ///< Add bitstream filters as requested by the muxer
 
+#define AVFMT_FLAG_ALLOW_CODEC_CHANGES 0x400000 ///< Allow AVStream.codecpar to be updated midstream if input changes (e.g. MPEG-TS ES stream_type changes)
+
     /**
      * Maximum number of bytes read from input in order to determine stream
      * properties. Used when reading the global header and in
diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
index deb69a0548..ed4ff580e5 100644
--- a/libavformat/mpegts.c
+++ b/libavformat/mpegts.c
@@ -2510,7 +2510,9 @@ static void pmt_cb(MpegTSFilter *filter, const uint8_t *section, int section_len
         if (!st)
             goto out;
 
-        if (pes && pes->stream_type != stream_type)
+        if (pes && (!pes->stream_type ||
+                    (pes->stream_type != stream_type &&
+                     !!(ts->stream->flags & AVFMT_FLAG_ALLOW_CODEC_CHANGES))))
             mpegts_set_stream_info(st, pes, stream_type, prog_reg_desc);
 
         add_pid_to_program(prg, pid);
diff --git a/libavformat/options_table.h b/libavformat/options_table.h
index e2e690fd2a..811dd342cc 100644
--- a/libavformat/options_table.h
+++ b/libavformat/options_table.h
@@ -50,6 +50,7 @@ static const AVOption avformat_options[] = {
 {"sortdts", "try to interleave outputted packets by dts", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_SORT_DTS }, INT_MIN, INT_MAX, D, .unit = "fflags"},
 {"fastseek", "fast but inaccurate seeks", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_FAST_SEEK }, INT_MIN, INT_MAX, D, .unit = "fflags"},
 {"nobuffer", "reduce the latency introduced by optional buffering", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_NOBUFFER }, 0, INT_MAX, D, .unit = "fflags"},
+{"allow_codec_changes", "allow AVStream.codecpar to change at runtime if input changes", 0, AV_OPT_TYPE_CONST, { .i64 = AVFMT_FLAG_ALLOW_CODEC_CHANGES }, 0, 0, D, .unit = "fflags" },
 {"bitexact", "do not write random/volatile data", 0, AV_OPT_TYPE_CONST, { .i64 = AVFMT_FLAG_BITEXACT }, 0, 0, E, .unit = "fflags" },
 {"autobsf", "add needed bsfs automatically", 0, AV_OPT_TYPE_CONST, { .i64 = AVFMT_FLAG_AUTO_BSF }, 0, 0, E, .unit = "fflags" },
 {"seek2any", "allow seeking to non-keyframes on demuxer level when supported", OFFSET(seek2any), AV_OPT_TYPE_BOOL, {.i64 = 0 }, 0, 1, D},
diff --git a/libavformat/version.h b/libavformat/version.h
index a7c80dc564..904e7f06aa 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -31,7 +31,7 @@
 
 #include "version_major.h"
 
-#define LIBAVFORMAT_VERSION_MINOR   1
+#define LIBAVFORMAT_VERSION_MINOR   2
 #define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
diff --git a/tests/fate/demux.mak b/tests/fate/demux.mak
index ead5ad4b10..e293a00dc0 100644
--- a/tests/fate/demux.mak
+++ b/tests/fate/demux.mak
@@ -158,7 +158,7 @@ FATE_SAMPLES_DEMUX-$(CONFIG_XWMA_DEMUXER) += fate-xwma-demux
 fate-xwma-demux: CMD = crc -i $(TARGET_SAMPLES)/xwma/ergon.xwma -c:a copy
 
 FATE_FFPROBE_DEMUX-$(CONFIG_MPEGTS_DEMUXER) += fate-ts-demux
-fate-ts-demux: CMD = ffprobe_demux $(TARGET_SAMPLES)/ac3/mp3ac325-4864-small.ts
+fate-ts-demux: CMD = ffprobe_demux $(TARGET_SAMPLES)/ac3/mp3ac325-4864-small.ts -fflags +allow_codec_changes
 
 FATE_FFPROBE_DEMUX-$(CONFIG_MPEGTS_DEMUXER) += fate-ts-timed-id3-demux
 fate-ts-timed-id3-demux: CMD = ffprobe_demux $(TARGET_SAMPLES)/mpegts/id3.ts
-- 
2.43.0