Re: [FFmpeg-devel] [PATCH v4] Add new method for playing network based streams with a play rate.

[Rashad Tatum <tatum.rashad@gmail.com>]

Thanks for the feedback. I'll look into it.

On Tue, Jun 3, 2025, 5:35 PM Andreas Rheinhardt <
andreas.rheinhardt@outlook.com> wrote:

> Rashad Tatum:
> > Add implementation for changing the play rate for rtsp streams.
> > ---
> >  libavformat/avformat.h    |  6 ++++++
> >  libavformat/demux.h       |  6 ++++++
> >  libavformat/demux_utils.c |  6 ++++++
> >  libavformat/rtsp.c        |  1 +
> >  libavformat/rtsp.h        | 10 ++++++++++
> >  libavformat/rtspdec.c     | 21 +++++++++++++++++++--
> >  6 files changed, 48 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> > index 2034d2aecc..7819b61d3e 100644
> > --- a/libavformat/avformat.h
> > +++ b/libavformat/avformat.h
> > @@ -2358,6 +2358,12 @@ int avformat_flush(AVFormatContext *s);
> >   */
> >  int av_read_play(AVFormatContext *s);
> >
> > +/**
> > + * Play a network-based stream (e.g. RTSP stream) with a given play rate
> > + * (e.g. Scale value for RTSP) and timestamp position.
> > + */
> > +int av_read_play_with_rate(AVFormatContext *s, double play_rate, int
> stream_index, int64_t timestamp);
> > +
> >  /**
> >   * Pause a network-based stream (e.g. RTSP stream).
> >   *
> > diff --git a/libavformat/demux.h b/libavformat/demux.h
> > index e83d84a201..965743bdf0 100644
> > --- a/libavformat/demux.h
> > +++ b/libavformat/demux.h
> > @@ -113,6 +113,12 @@ typedef struct FFInputFormat {
> >       * (RTSP).
> >       */
> >      int (*read_play)(struct AVFormatContext *);
> > +
> > +    /**
> > +     * Play a network-based stream (e.g. RTSP stream) with a given play
> rate
> > +     * (e.g. Scale value for RTSP) and timestamp position.
> > +     */
> > +    int (*read_play_with_rate)(struct AVFormatContext *s, double
> play_rate, int stream_index, int64_t timestamp);
> >
> >      /**
> >       * Pause playing - only meaningful if using a network-based format
> > diff --git a/libavformat/demux_utils.c b/libavformat/demux_utils.c
> > index b632277460..8fed41e3b6 100644
> > --- a/libavformat/demux_utils.c
> > +++ b/libavformat/demux_utils.c
> > @@ -179,6 +179,12 @@ int av_read_play(AVFormatContext *s)
> >      return AVERROR(ENOSYS);
> >  }
> >
> > +int av_read_play_with_rate(AVFormatContext *s, double play_rate, int
> stream_index, int64_t timestamp) {
> > +    if (ffifmt(s->iformat)->read_play_with_rate)
> > +        return ffifmt(s->iformat)->read_play_with_rate(s, play_rate,
> stream_index, timestamp);
> > +    return AVERROR(ENOSYS);
> > +}
> > +
> >  int av_read_pause(AVFormatContext *s)
> >  {
> >      if (ffifmt(s->iformat)->read_pause)
> > diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
> > index 5ea471b40c..6cfbcdf989 100644
> > --- a/libavformat/rtsp.c
> > +++ b/libavformat/rtsp.c
> > @@ -1998,6 +1998,7 @@ redirect:
> >      av_strlcpy(rt->real_challenge, real_challenge,
> sizeof(rt->real_challenge));
> >      rt->state = RTSP_STATE_IDLE;
> >      rt->seek_timestamp = 0; /* default is to start stream at position
> zero */
> > +    rt->scale = 1.0; /* default is to play at the normal rate */
> >      return 0;
> >   fail:
> >      ff_rtsp_close_streams(s);
> > diff --git a/libavformat/rtsp.h b/libavformat/rtsp.h
> > index 83b2e3f4fb..1b8ce05d74 100644
> > --- a/libavformat/rtsp.h
> > +++ b/libavformat/rtsp.h
> > @@ -245,6 +245,16 @@ typedef struct RTSPState {
> >       * whenever we resume playback. Either way, the value is only used
> once,
> >       * see rtsp_read_play() and rtsp_read_seek(). */
> >      int64_t seek_timestamp;
> > +
> > +    /** the scale value requested when calling av_read_play(). This
> value
> > +     * is subsequently used as part of the "Scale" parameter when
> emitting
> > +     * the RTSP PLAY command. The "Scale" parameter determines the
> stream play
> > +     * rate. A value of 1 represents the normal play rate. Any other
> value is
> > +     * in regards to the normal play rate. A negative value represents
> reverse
> > +     * playback. If we are currently playing, this command is called
> instantly.
> > +     * If we are currently paused, this command is called whenever we
> resume
> > +     * playback.  */
> > +    double scale;
> >
> >      int seq;                          /**< RTSP command sequence number
> */
> >
> > diff --git a/libavformat/rtspdec.c b/libavformat/rtspdec.c
> > index 10078ce2fa..f1e44ccb63 100644
> > --- a/libavformat/rtspdec.c
> > +++ b/libavformat/rtspdec.c
> > @@ -39,6 +39,7 @@
> >  #include "tls.h"
> >  #include "url.h"
> >  #include "version.h"
> > +#include <stdio.h>
> >
> >  static const struct RTSPStatusMessage {
> >      enum RTSPStatusCode code;
> > @@ -527,7 +528,7 @@ static int rtsp_read_play(AVFormatContext *s)
> >  {
> >      RTSPState *rt = s->priv_data;
> >      RTSPMessageHeader reply1, *reply = &reply1;
> > -    int i;
> > +    int i, cmd_char_count = 0;
> >      char cmd[MAX_URL_SIZE];
> >
> >      av_log(s, AV_LOG_DEBUG, "hello state=%d\n", rt->state);
> > @@ -564,11 +565,17 @@ static int rtsp_read_play(AVFormatContext *s)
> >          if (rt->state == RTSP_STATE_PAUSED) {
> >              cmd[0] = 0;
> >          } else {
> > -            snprintf(cmd, sizeof(cmd),
> > +
> > +            cmd_char_count += snprintf(cmd, sizeof(cmd),
> >                       "Range: npt=%"PRId64".%03"PRId64"-\r\n",
> >                       rt->seek_timestamp / AV_TIME_BASE,
> >                       rt->seek_timestamp / (AV_TIME_BASE / 1000) % 1000);
> > +
> > +            snprintf(cmd + cmd_char_count, sizeof(cmd) -
> cmd_char_count, "Scale: %f\r\n", rt->scale);
> > +
> >          }
> > +
> > +
> >          ff_rtsp_send_cmd(s, "PLAY", rt->control_uri, cmd, reply, NULL);
> >          if (reply->status_code != RTSP_STATUS_OK) {
> >              return ff_rtsp_averror(reply->status_code, -1);
> > @@ -593,6 +600,15 @@ static int rtsp_read_play(AVFormatContext *s)
> >      return 0;
> >  }
> >
> > +static int rtsp_read_play_with_rate(AVFormatContext *s, double
> play_rate, int stream_index, int64_t timestamp) {
> > +    RTSPState *rt = s->priv_data;
> > +    rt->seek_timestamp = av_rescale_q(timestamp,
> > +
> s->streams[stream_index]->time_base,
> > +                                      AV_TIME_BASE_Q);
> > +    rt->scale = play_rate;
> > +    return rtsp_read_play(s);
> > +}
> > +
> >  /* pause the stream */
> >  static int rtsp_read_pause(AVFormatContext *s)
> >  {
> > @@ -1006,5 +1022,6 @@ const FFInputFormat ff_rtsp_demuxer = {
> >      .read_close     = rtsp_read_close,
> >      .read_seek      = rtsp_read_seek,
> >      .read_play      = rtsp_read_play,
> > +    .read_play_with_rate = rtsp_read_play_with_rate,
> >      .read_pause     = rtsp_read_pause,
> >  };
>
> Seems like play_rate should just be an option of this demuxer (with the
> AV_OPT_FLAG_RUNTIME_PARAM flag).
>
> - Andreas
>
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