Re: [FFmpeg-devel] [PATCH] avformat: set start_time_realtime when demuxing

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Gyan Doshi:
> Add new flag AVFMT_START_REALTIME for the couple of demuxers that set it
> internally.
> ---
>  doc/APIchanges         | 3 +++
>  libavformat/avformat.h | 1 +
>  libavformat/demux.c    | 3 +++
>  libavformat/rtsp.c     | 3 ++-
>  libavformat/version.h  | 2 +-
>  5 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/doc/APIchanges b/doc/APIchanges
> index 5857e67ae6..4aa9e36777 100644
> --- a/doc/APIchanges
> +++ b/doc/APIchanges
> @@ -14,6 +14,9 @@ libavutil:     2021-04-27
>  
>  API changes, most recent first:
>  
> +2022-06-xx - xxxxxxxxxx - lavf 59.26.100 - avformat.h
> +  Add AVFMT_START_REALTIME flag.
> +
>  2022-06-12 - xxxxxxxxxx - lavf 59.25.100 - avio.h
>    Add avio_vprintf(), similar to avio_printf() but allow to use it
>    from within a function taking a variable argument list as input.
> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> index f12fa7d904..4e247d68fc 100644
> --- a/libavformat/avformat.h
> +++ b/libavformat/avformat.h
> @@ -499,6 +499,7 @@ typedef struct AVProbeData {
>                                          The user or muxer can override this through
>                                          AVFormatContext.avoid_negative_ts
>                                          */
> +#define AVFMT_START_REALTIME 0x80000 /**< Demuxer sets start_time_realtime */

This is incorrect: If this were merged, start_time_realtime would always
be set by libavformat; whether it is done by the generic code or by
demuxer specific code is an implementation detail and irrelevant for the
user. Given that it is also set for demuxers without this flag actually
means that libavformat lies when using a demuxer without this flag.

>  
>  #define AVFMT_SEEK_TO_PTS   0x4000000 /**< Seeking is based on PTS */
>  
> diff --git a/libavformat/demux.c b/libavformat/demux.c
> index 1620716716..28c6966e71 100644
> --- a/libavformat/demux.c
> +++ b/libavformat/demux.c
> @@ -628,6 +628,9 @@ FF_ENABLE_DEPRECATION_WARNINGS
>  
>          force_codec_ids(s, st);
>  
> +        if (!(s->iformat->flags & AVFMT_START_REALTIME) && s->start_time_realtime == AV_NOPTS_VALUE)
> +            s->start_time_realtime = av_gettime();
> +
>          /* TODO: audio: time filter; video: frame reordering (pts != dts) */
>          if (s->use_wallclock_as_timestamps)
>              pkt->dts = pkt->pts = av_rescale_q(av_gettime(), AV_TIME_BASE_Q, st->time_base);
> diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
> index 88e9ef5226..2cafe33887 100644
> --- a/libavformat/rtsp.c
> +++ b/libavformat/rtsp.c
> @@ -2489,6 +2489,7 @@ const AVInputFormat ff_sdp_demuxer = {
>      .read_header    = sdp_read_header,
>      .read_packet    = ff_rtsp_fetch_packet,
>      .read_close     = sdp_read_close,
> +    .flags          = AVFMT_START_REALTIME,
>      .priv_class     = &sdp_demuxer_class,
>  };
>  #endif /* CONFIG_SDP_DEMUXER */
> @@ -2648,7 +2649,7 @@ const AVInputFormat ff_rtp_demuxer = {
>      .read_header    = rtp_read_header,
>      .read_packet    = ff_rtsp_fetch_packet,
>      .read_close     = sdp_read_close,
> -    .flags          = AVFMT_NOFILE,
> +    .flags          = AVFMT_NOFILE | AVFMT_START_REALTIME,
>      .priv_class     = &rtp_demuxer_class,
>  };
>  #endif /* CONFIG_RTP_DEMUXER */
> diff --git a/libavformat/version.h b/libavformat/version.h
> index 966ebb7ed3..0708d619c0 100644
> --- a/libavformat/version.h
> +++ b/libavformat/version.h
> @@ -31,7 +31,7 @@
>  
>  #include "version_major.h"
>  
> -#define LIBAVFORMAT_VERSION_MINOR  25
> +#define LIBAVFORMAT_VERSION_MINOR  26
>  #define LIBAVFORMAT_VERSION_MICRO 100
>  
>  #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \

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