avformat/rtpdec: Avoid allocations of small dynamic buffers

Besides avoiding allocations this also fixes a design defect of
ff_rtp_send_punch_packets: It did not return an error in case of
these allocations failed.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/rtpdec.c

@@ -404,38 +404,26 @@ int ff_rtp_check_and_send_back_rr(RTPDemuxContext *s, URLContext *fd,
 
 void ff_rtp_send_punch_packets(URLContext *rtp_handle)
 {
-    AVIOContext *pb;
-    uint8_t *buf;
-    int len;
+    uint8_t buf[RTP_MIN_PACKET_LENGTH], *ptr = buf;
 
     /* Send a small RTP packet */
-    if (avio_open_dyn_buf(&pb) < 0)
-        return;
 
-    avio_w8(pb, (RTP_VERSION << 6));
-    avio_w8(pb, 0); /* Payload type */
-    avio_wb16(pb, 0); /* Seq */
-    avio_wb32(pb, 0); /* Timestamp */
-    avio_wb32(pb, 0); /* SSRC */
+    bytestream_put_byte(&ptr, (RTP_VERSION << 6));
+    bytestream_put_byte(&ptr, 0); /* Payload type */
+    bytestream_put_be16(&ptr, 0); /* Seq */
+    bytestream_put_be32(&ptr, 0); /* Timestamp */
+    bytestream_put_be32(&ptr, 0); /* SSRC */
 
-    len = avio_close_dyn_buf(pb, &buf);
-    if ((len > 0) && buf)
-        ffurl_write(rtp_handle, buf, len);
-    av_free(buf);
+    ffurl_write(rtp_handle, buf, ptr - buf);
 
     /* Send a minimal RTCP RR */
-    if (avio_open_dyn_buf(&pb) < 0)
-        return;
+    ptr = buf;
+    bytestream_put_byte(&ptr, (RTP_VERSION << 6));
+    bytestream_put_byte(&ptr, RTCP_RR); /* receiver report */
+    bytestream_put_be16(&ptr, 1); /* length in words - 1 */
+    bytestream_put_be32(&ptr, 0); /* our own SSRC */
 
-    avio_w8(pb, (RTP_VERSION << 6));
-    avio_w8(pb, RTCP_RR); /* receiver report */
-    avio_wb16(pb, 1); /* length in words - 1 */
-    avio_wb32(pb, 0); /* our own SSRC */
-
-    len = avio_close_dyn_buf(pb, &buf);
-    if ((len > 0) && buf)
-        ffurl_write(rtp_handle, buf, len);
-    av_free(buf);
+    ffurl_write(rtp_handle, buf, ptr - buf);
 }
 
 static int find_missing_packets(RTPDemuxContext *s, uint16_t *first_missing,