Re: [FFmpeg-devel] [PATCH] avformat/mpegts: Add AVFMT_FLAG_ALLOW_CODEC_CHANGES (v2)

[Scott Theisen <scott.the.elm-at-gmail.com@ffmpeg.org>]

On 2025/06/29 23:55, Pavel Koshevoy wrote:
> 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.

Is this signaled in any way or is the client expected to check if 
codecpar has changed?

I ask because MythTV added checking and a callback for streams changing 
between PMT versions, including adding or removing streams.

Thanks,

Scott Theisen

> ---
>   doc/APIchanges          | 3 +++
>   libavformat/avformat.h  | 2 ++
>   libavformat/mpegts.c    | 4 +++-
>   libavformat/version.h   | 4 ++--
>   tests/ref/fate/ts-demux | 4 ++--
>   5 files changed, 12 insertions(+), 5 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/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/version.h b/libavformat/version.h
> index b32ddb3617..904e7f06aa 100644
> --- a/libavformat/version.h
> +++ b/libavformat/version.h
> @@ -31,8 +31,8 @@
>   
>   #include "version_major.h"
>   
> -#define LIBAVFORMAT_VERSION_MINOR   1
> -#define LIBAVFORMAT_VERSION_MICRO 101
> +#define LIBAVFORMAT_VERSION_MINOR   2
> +#define LIBAVFORMAT_VERSION_MICRO 100
>   
>   #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
>                                                  LIBAVFORMAT_VERSION_MINOR, \
> diff --git a/tests/ref/fate/ts-demux b/tests/ref/fate/ts-demux
> index d56cc27937..6a830d0d99 100644
> --- a/tests/ref/fate/ts-demux
> +++ b/tests/ref/fate/ts-demux
> @@ -24,6 +24,6 @@ packet|codec_type=video|stream_index=0|pts=3912686363|pts_time=43474.292922|dts=
>   packet|codec_type=audio|stream_index=1|pts=3912644825|pts_time=43473.831389|dts=3912644825|dts_time=43473.831389|duration=2880|duration_time=0.032000|size=906|pos=474888|flags=K__|data_hash=CRC32:0893d398
>   packet|codec_type=audio|stream_index=2|pts=3912645580|pts_time=43473.839778|dts=3912645580|dts_time=43473.839778|duration=2880|duration_time=0.032000|size=354|pos=491808|flags=K__|data_hash=CRC32:f5963fa6
>   stream|index=0|codec_name=mpeg2video|profile=4|codec_type=video|codec_tag_string=[2][0][0][0]|codec_tag=0x0002|width=1280|height=720|coded_width=0|coded_height=0|has_b_frames=1|sample_aspect_ratio=1:1|display_aspect_ratio=16:9|pix_fmt=yuv420p|level=4|color_range=tv|color_space=unknown|color_transfer=unknown|color_primaries=unknown|chroma_location=left|field_order=progressive|refs=1|ts_id=32776|ts_packetsize=188|id=0x31|r_frame_rate=60000/1001|avg_frame_rate=60000/1001|time_base=1/90000|start_pts=3912669846|start_time=43474.109400|duration_ts=19519|duration=0.216878|bit_rate=15000000|max_bit_rate=N/A|bits_per_raw_sample=N/A|nb_frames=N/A|nb_read_frames=N/A|nb_read_packets=15|extradata_size=150|extradata_hash=CRC32:53134fa8|disposition:default=0|disposition:dub=0|disposition:original=0|disposition:comment=0|disposition:lyrics=0|disposition:karaoke=0|disposition:forced=0|disposition:hearing_impaired=0|disposition:visual_impaired=0|disposition:clean_effects=0|disposition:attached_pic
 =0|
>   disposition:timed_thumbnails=0|disposition:non_diegetic=0|disposition:captions=0|disposition:descriptions=0|disposition:metadata=0|disposition:dependent=0|disposition:still_image=0|disposition:multilayer=0|side_datum/cpb_properties:side_data_type=CPB properties|side_datum/cpb_properties:max_bitrate=15000000|side_datum/cpb_properties:min_bitrate=0|side_datum/cpb_properties:avg_bitrate=0|side_datum/cpb_properties:buffer_size=9781248|side_datum/cpb_properties:vbv_delay=-1
> -stream|index=1|codec_name=ac3|profile=unknown|codec_type=audio|codec_tag_string=[6][0][0][0]|codec_tag=0x0006|sample_fmt=fltp|sample_rate=48000|channels=6|channel_layout=5.1(side)|bits_per_sample=0|initial_padding=0|dmix_mode=0|ltrt_cmixlev=0.000000|ltrt_surmixlev=0.000000|loro_cmixlev=0.000000|loro_surmixlev=0.000000|ts_id=32776|ts_packetsize=188|id=0x34|r_frame_rate=0/0|avg_frame_rate=0/0|time_base=1/90000|start_pts=3912633305|start_time=43473.703389|duration_ts=14400|duration=0.160000|bit_rate=384000|max_bit_rate=N/A|bits_per_raw_sample=N/A|nb_frames=N/A|nb_read_frames=N/A|nb_read_packets=5|disposition:default=0|disposition:dub=0|disposition:original=0|disposition:comment=0|disposition:lyrics=0|disposition:karaoke=0|disposition:forced=0|disposition:hearing_impaired=0|disposition:visual_impaired=0|disposition:clean_effects=0|disposition:attached_pic=0|disposition:timed_thumbnails=0|disposition:non_diegetic=0|disposition:captions=0|disposition:descriptions=0|disposition:metadata=
 0|
>   disposition:dependent=0|disposition:still_image=0|disposition:multilayer=0|tag:language=eng
> -stream|index=2|codec_name=ac3|profile=unknown|codec_type=audio|codec_tag_string=[6][0][0][0]|codec_tag=0x0006|sample_fmt=fltp|sample_rate=48000|channels=2|channel_layout=stereo|bits_per_sample=0|initial_padding=0|dmix_mode=0|ltrt_cmixlev=0.000000|ltrt_surmixlev=0.000000|loro_cmixlev=0.000000|loro_surmixlev=0.000000|ts_id=32776|ts_packetsize=188|id=0x35|r_frame_rate=0/0|avg_frame_rate=0/0|time_base=1/90000|start_pts=3912634060|start_time=43473.711778|duration_ts=14400|duration=0.160000|bit_rate=192000|max_bit_rate=N/A|bits_per_raw_sample=N/A|nb_frames=N/A|nb_read_frames=N/A|nb_read_packets=5|disposition:default=0|disposition:dub=0|disposition:original=0|disposition:comment=0|disposition:lyrics=0|disposition:karaoke=0|disposition:forced=0|disposition:hearing_impaired=0|disposition:visual_impaired=0|disposition:clean_effects=0|disposition:attached_pic=0|disposition:timed_thumbnails=0|disposition:non_diegetic=0|disposition:captions=0|disposition:descriptions=0|disposition:metadata=0|d
 is
>   position:dependent=0|disposition:still_image=0|disposition:multilayer=0|tag:language=es
> +stream|index=1|codec_name=ac3|profile=unknown|codec_type=audio|codec_tag_string=[4][0][0][0]|codec_tag=0x0004|sample_fmt=fltp|sample_rate=48000|channels=6|channel_layout=5.1(side)|bits_per_sample=0|initial_padding=0|dmix_mode=0|ltrt_cmixlev=0.000000|ltrt_surmixlev=0.000000|loro_cmixlev=0.000000|loro_surmixlev=0.000000|ts_id=32776|ts_packetsize=188|id=0x34|r_frame_rate=0/0|avg_frame_rate=0/0|time_base=1/90000|start_pts=3912633305|start_time=43473.703389|duration_ts=14400|duration=0.160000|bit_rate=384000|max_bit_rate=N/A|bits_per_raw_sample=N/A|nb_frames=N/A|nb_read_frames=N/A|nb_read_packets=5|disposition:default=0|disposition:dub=0|disposition:original=0|disposition:comment=0|disposition:lyrics=0|disposition:karaoke=0|disposition:forced=0|disposition:hearing_impaired=0|disposition:visual_impaired=0|disposition:clean_effects=0|disposition:attached_pic=0|disposition:timed_thumbnails=0|disposition:non_diegetic=0|disposition:captions=0|disposition:descriptions=0|disposition:metadata=
 0|
>   disposition:dependent=0|disposition:still_image=0|disposition:multilayer=0|tag:language=eng
> +stream|index=2|codec_name=ac3|profile=unknown|codec_type=audio|codec_tag_string=[4][0][0][0]|codec_tag=0x0004|sample_fmt=fltp|sample_rate=48000|channels=2|channel_layout=stereo|bits_per_sample=0|initial_padding=0|dmix_mode=0|ltrt_cmixlev=0.000000|ltrt_surmixlev=0.000000|loro_cmixlev=0.000000|loro_surmixlev=0.000000|ts_id=32776|ts_packetsize=188|id=0x35|r_frame_rate=0/0|avg_frame_rate=0/0|time_base=1/90000|start_pts=3912634060|start_time=43473.711778|duration_ts=14400|duration=0.160000|bit_rate=192000|max_bit_rate=N/A|bits_per_raw_sample=N/A|nb_frames=N/A|nb_read_frames=N/A|nb_read_packets=5|disposition:default=0|disposition:dub=0|disposition:original=0|disposition:comment=0|disposition:lyrics=0|disposition:karaoke=0|disposition:forced=0|disposition:hearing_impaired=0|disposition:visual_impaired=0|disposition:clean_effects=0|disposition:attached_pic=0|disposition:timed_thumbnails=0|disposition:non_diegetic=0|disposition:captions=0|disposition:descriptions=0|disposition:metadata=0|d
 is
>   position:dependent=0|disposition:still_image=0|disposition:multilayer=0|tag:language=es
>   format|filename=mp3ac325-4864-small.ts|nb_streams=3|nb_programs=1|nb_stream_groups=0|format_name=mpegts|start_time=43473.703389|duration=0.622889|size=512000|bit_rate=6575810|probe_score=50

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