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

* [FFmpeg-devel] [PATCH v4] Add new method for playing network based streams with a play rate.
@ 2025-06-03 16:49 Rashad Tatum
  2025-06-03 21:35 ` Andreas Rheinhardt
  0 siblings, 1 reply; 3+ messages in thread
From: Rashad Tatum @ 2025-06-03 16:49 UTC (permalink / raw)
  To: ffmpeg-devel; +Cc: 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,
 };
-- 
2.49.0

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