Fix: ts for audio frame matches the RTP ts of the 1st pkt (#1243)

Set timestamp to the RTP timestamp of the first packet of the audio
frame
 (not the last one like currently) in st30 to ensure lipsync.

---------

Co-authored-by: Wesierski, Dawid <[email protected]>

Author: Magda-Pytel

lib/src/st2110/st_header.h

@@ -1019,6 +1019,7 @@ struct st_rx_audio_session_impl {
   int st30_pkt_idx;       /* pkt index in current frame */
   int latest_seq_id;      /* latest seq id */
 
+  uint32_t first_pkt_rtp_ts; /* rtp time stamp for the first pkt */
   uint32_t tmstamp;
   size_t frame_recv_size;
 

lib/src/st2110/st_rx_audio_session.c

@@ -269,6 +269,7 @@ static int rx_audio_session_handle_frame_pkt(struct mtl_main_impl* impl,
 
     return -EINVAL;
   }
+
   if (ops->ssrc) {
     uint32_t ssrc = ntohl(rtp->ssrc);
     if (ssrc != ops->ssrc) {
@@ -287,6 +288,10 @@ static int rx_audio_session_handle_frame_pkt(struct mtl_main_impl* impl,
     return -EINVAL;
   }
 
+  if (s->st30_pkt_idx == 0) {
+    s->first_pkt_rtp_ts = tmstamp;
+  }
+
   /* set first seq_id - 1 */
   if (unlikely(s->latest_seq_id == -1)) s->latest_seq_id = seq_id - 1;
   /* drop old packet */
@@ -359,15 +364,15 @@ static int rx_audio_session_handle_frame_pkt(struct mtl_main_impl* impl,
     }
 
     meta->tfmt = ST10_TIMESTAMP_FMT_MEDIA_CLK;
-    meta->timestamp = tmstamp;
+    meta->timestamp = s->first_pkt_rtp_ts;
     meta->fmt = ops->fmt;
     meta->sampling = ops->sampling;
     meta->channel = ops->channel;
-    meta->rtp_timestamp = tmstamp;
+    meta->rtp_timestamp = s->first_pkt_rtp_ts;
     meta->frame_recv_size = s->frame_recv_size;
 
-    MT_USDT_ST30_RX_FRAME_AVAILABLE(s->mgr->idx, s->idx, frame->idx, frame->addr, tmstamp,
-                                    meta->frame_recv_size);
+    MT_USDT_ST30_RX_FRAME_AVAILABLE(s->mgr->idx, s->idx, frame->idx, frame->addr,
+                                    s->first_pkt_rtp_ts, meta->frame_recv_size);
     /* check if dump USDT enabled */
     if (MT_USDT_ST30_RX_FRAME_DUMP_ENABLED()) {
       rx_audio_session_usdt_dump_frame(s, frame);