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gst-nmos-rs: emit ST 2110-40 SSN in synthesised ANC SDP #111

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Merged
garethsb merged 1 commit into from
Aug 20, 2026
Merged

gst-nmos-rs: emit ST 2110-40 SSN in synthesised ANC SDP #111

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29 changes: 28 additions & 1 deletion rust/gst-nmos-rs/src/sdp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -195,6 +195,12 @@ pub(crate) mod defaults {
/// to. `ST2110-22:2022` is what nmos-cpp emits for `video/jxsv`.
pub(crate) const ST2110_22_SSN: &str = "ST2110-22:2022";

/// ST 2110-40 §7 required `SSN` parameter. Identifies the SDP
/// specification revision the ANC sender conforms to. Default
/// `ST2110-40:2018` matches nmos-cpp when `TM` is omitted;
/// `ST2110-40:2023` is required when signalling `TM`.
pub(crate) const ST2110_40_SSN: &str = "ST2110-40:2018";

// ST 2110-21 §8.1 `TP` (type parameter) is intentionally omitted
// from caps-only **video** synthesis for now — see
// [`rtp_caps_from_video`]. Without `TP=2110TPW` or `TP=2110TPN`
Expand Down Expand Up @@ -2722,6 +2728,11 @@ fn rtp_caps_from_audio(
/// | (fixed) | `media=video`, `encoding-name=SMPTE291` |
/// | `framerate` (optional) | `exactframerate` |
///
/// Always-emitted ST 2110-40 §7 fmtp parameter:
/// `ssn=ST2110-40:2018` (see [`defaults::ST2110_40_SSN`]). Optional
/// RFC 8331 / ST 2110-40 fmtp (`VPID_Code`, repeated `DID_SDID`,
/// `TM`) are not synthesised from essence caps.
///
/// ANC is carried on `m=video` per RFC 8331 §3; the dispatch
/// over to ANC handling is keyed off `encoding-name=SMPTE291`
/// in [`parse_sdp`].
Expand All @@ -2743,14 +2754,18 @@ fn rtp_caps_from_data(caps: &gst::Caps, payload_type: u8) -> Result<gst::Caps, S
)));
}
let framerate = s.get::<gst::Fraction>("framerate").ok();
// Fmtp keys are lower-case in caps (`ssn`); SDP upper-case
// `SSN` is restored by [`canonicalise_st2110_sdp_case`].
let mut caps_text = format!(
"application/x-rtp,\
media=(string)video,\
clock-rate=(int){clk},\
encoding-name=(string)SMPTE291,\
payload=(int){pt}",
payload=(int){pt},\
ssn=(string){ssn}",
clk = defaults::ANC_CLOCK_RATE,
pt = payload_type,
ssn = defaults::ST2110_40_SSN,
);
if let Some(f) = framerate {
let exactframerate = format_exact_framerate(f.numer() as u32, f.denom() as u32);
Expand Down Expand Up @@ -5334,6 +5349,7 @@ mod tests {
defaults::ANC_CLOCK_RATE
);
assert_eq!(s.get::<i32>("payload").unwrap(), 100);
assert_eq!(s.get::<&str>("ssn").unwrap(), defaults::ST2110_40_SSN);
assert!(
s.get::<&str>("exactframerate").is_err(),
"ANC without framerate must omit `exactframerate=`",
Expand Down Expand Up @@ -5395,6 +5411,13 @@ mod tests {
assert_eq!(defaults::ST2110_20_SSN, "ST2110-20:2017");
}

#[test]
fn defaults_st2110_40_ssn_matches_nmos_cpp() {
// nmos-cpp `make_video_smpte291_parameters` emits
// `ST2110-40:2018` when `TM` is omitted (ST 2110-40 §7).
assert_eq!(defaults::ST2110_40_SSN, "ST2110-40:2018");
}

/// `colorimetry` is REQUIRED by nmos-cpp's
/// `get_video_raw_parameters` and the SMPTE ST 2110-20
/// reference SDPs all use `BT709` for SDR. Keep the default
Expand Down Expand Up @@ -6096,6 +6119,10 @@ mod tests {
"ANC rtpmap must be lower-case in the SDP per RFC 8331 §3.1 / §4:\n{text}",
);
assert!(text.contains("exactframerate=25"));
assert!(
text.contains("SSN=ST2110-40:2018"),
"ST 2110-40 §7 required SSN:\n{text}",
);
}

#[test]
Expand Down
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