Theoretical possibility of accessing substream XML metadata either directly or after teardown of primary stream.

[Andy Gee]

I'm using openRTSP to read the VND.ONVIF.METADATA metadata stream from
a camera source. My use case involves as many cameras as possible
simultaneously however the bandwidth requirements for this is
excessive.

Is it possible to request only the VND.ONVIF.METADATA/8000 substream
without requesting the video, or, to cancel the video and continue to
read the XML substream?
If so, what RTP or event HTTP requests would I send to achieve this?
Currently I'm using openRTSP as it's the most stable

openRTSP -K -t rtsp://user:password@192.168.2.4:5554/live/ch3

I have a cron job to delete the generated `video-H264-1` but this does
not help with the bandwidth problem from 40+ cameras.

I guess I'm asking if it's theoretically possible to request only the
metadata before I start to learn C and start tinkering with openRTSP.

I would really appreciate your help.

Andy Gee

Redacted wireshark cap for context
---------------------


OPTIONS rtsp://user:password@192.168.2.4:5554/live/ch3 RTSP/1.0
CSeq: 2
User-Agent: openRTSP (LIVE555 Streaming Media v2020.01.19)

RTSP/1.0 200 OK
CSeq: 2
Public: OPTIONS, DESCRIBE, SETUP, TEARDOWN, PLAY, PAUSE,
GET_PARAMETER, SET_PARAMETER

DESCRIBE rtsp://user:password@192.168.2.4:5554/live/ch3 RTSP/1.0
CSeq: 3
User-Agent: openRTSP (LIVE555 Streaming Media v2020.01.19)
Accept: application/sdp

RTSP/1.0 401 Unauthorized
CSeq: 3
WWW-Authenticate: Digest realm="ITX_VABOX",
nonce="624f4713ded27e27fa1d7080377ea08f7539xxxxxxxxxxxxxxxxxxxxxxxxxxx"

DESCRIBE rtsp://user:password@192.168.2.4:5554/live/ch3 RTSP/1.0
CSeq: 4
Authorization: Digest username="user", realm="ITX_VABOX",
nonce="624f4713ded27e27fa1d7080377ea08f7539xxxxxxxxxxxxxxxxxxxxxxxxxxx",
uri="rtsp://user:password@192.168.2.4:5554/live/ch3",
response="6ff5ee5585714bdec5e9d0881ac50f13"
User-Agent: openRTSP (LIVE555 Streaming Media v2020.01.19)
Accept: application/sdp

RTSP/1.0 200 OK
CSeq: 4
Content-Base: rtsp://user:password@192.168.2.4:5554/live/ch3
Content-Type: application/sdp
Content-Length: 447

v=0
o=- 1 1 IN IP4 192.168.2.4
s=Media Server
t=0 0
a=type:broadcast
c=IN IP4 0.0.0.0
m=video 0 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 packetization-mode=1;profile-level-id=64001F;sprop-parameter-sets=Z0IAKpY1QPAET8s3BQEFAg==,aM48gA==
a=control:rtsp://user:password@192.168.2.4:5554/live/ch3/video
m=application 0 RTP/AVP 97
a=rtpmap:97 VND.ONVIF.METADATA/8000
a=control:rtsp://user:password@192.168.2.4:5554/live/ch3/meta
SETUP rtsp://user:password@192.168.2.4:5554/live/ch3/video RTSP/1.0
CSeq: 5
Authorization: Digest username="user", realm="ITX_VABOX",
nonce="624f4713ded27e27fa1d7080377ea08f7539xxxxxxxxxxxxxxxxxxxxxxxxxxx",
uri="rtsp://user:password@192.168.2.4:5554/live/ch3",
response="db905a19d453ae8c12eb6dce29bda69d"
User-Agent: openRTSP (LIVE555 Streaming Media v2020.01.19)
Transport: RTP/AVP/TCP;unicast;interleaved=0-1

RTSP/1.0 200 OK
CSeq: 5
Transport: RTP/AVP/TCP;unicast;interleaved=0-1
Session: 1F5864785080127168A98B87625988;timeout=60

SETUP rtsp://user:password@192.168.2.4:5554/live/ch3/meta RTSP/1.0
CSeq: 6
Authorization: Digest username="user", realm="ITX_VABOX",
nonce="624f4713ded27e27fa1d7080377ea08f7539xxxxxxxxxxxxxxxxxxxxxxxxxxx",
uri="rtsp://user:password@192.168.2.4:5554/live/ch3",
response="db905a19d453ae8c12eb6dce29bda69d"
User-Agent: openRTSP (LIVE555 Streaming Media v2020.01.19)
Transport: RTP/AVP/TCP;unicast;interleaved=2-3
Session: 1F5864785080127168A98B87625988

RTSP/1.0 200 OK
CSeq: 6
Transport: RTP/AVP/TCP;unicast;interleaved=2-3
Session: 1F5864785080127168A98B87625988;timeout=60

PLAY rtsp://user:password@192.168.2.4:5554/live/ch3 RTSP/1.0
CSeq: 7
Authorization: Digest username="user", realm="ITX_VABOX",
nonce="624f4713ded27e27fa1d7080377ea08f7539xxxxxxxxxxxxxxxxxxxxxxxxxxx",
uri="rtsp://user:password@192.168.2.4:5554/live/ch3",
response="08fa749bd58008332adf03e0e2683385"
User-Agent: openRTSP (LIVE555 Streaming Media v2020.01.19)
Session: 1F5864785080127168A98B87625988
Range: npt=0.000-

RTSP/1.0 200 OK
CSeq: 7
Session: 1F5864785080127168A98B87625988
Range: clock=20220407T201720.300Z-
RTP-Info: url=rtsp://user:password@192.168.2.4:5554/live/ch3/video?;seq=29232;rtptime=2325753720,url=rtsp://user:password@192.168.2.4:5554/live/ch3/meta?;seq=29232;rtptime=2328508980

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data flows.........