Add VLC SAP message support

[dbussert]

SAP messages for MPEG-TS UDP video have a /x to the port like 8208/1. Wireshark calls this Media Port Count. The media filter of \d does not match this, so it's not parsed. This pull request adds a grammar regex that matches a line like m=video 8208/1 udp 33

[clux]

Ah, thanks for this.

I think it's probably better to widen the existing regex to capture it if that's possible. AFAIKT it's only the \d that's causing the problem, and everything else is identical. I'd rather not have more than one m line regex because m-line semantics is kind of wild.

A quick test sdp for this would be very helpful.

[dbussert]

do you want the regex to be \d and only the char / to be minimalist?

[clux]

i think you can still have something that is effectively (\d*)/(*/d), but that only gets the port count parameter if there's a slash

possibly (\d*)(?:\/(\d*)).. the rfc4566 indicates that this is all within-spec, and we should have had support in the first place.

[ibc]

Please don't add a new grammar rule just to parse an optional field that was missing in the existing grammar rule.

[dbussert]

finally got around to integrating those 2 rules together. I ended up with /^(\w*) (\d*)(?:\/(\d*))? ([\w/]*)(?: (.*))?/ which adds an optional match for a port number while excluding the / divider with a non-matching group

No port count makes portCount undefined

'video 8208 udp 33'.match(/^(\w*) (\d*)(?:\/(\d*))? ([\w/]*)(?: (.*))?/)
(6) ["video 8208 udp 33", "video", "8208", undefined, "udp", "33", index: 0, input: "video 8208 udp 33", groups: undefined]

A / and port count after the port is now captured

'video 8208/1 udp 33'.match(/^(\w*) (\d*)(?:\/(\d*))? ([\w/]*)(?: (.*))?/)
(6) ["video 8208/1 udp 33", "video", "8208", "1", "udp", "33", index: 0, input: "video 8208/1 udp 33", groups: undefined]

The one issue is with \d* it will capture an empty string if there is a / but no port count defined

'video 8208/ udp 33'.match(/^(\w*) (\d*)(?:\/(\d*))? ([\w/]*)(?: (.*))?/)
(6) ["video 8208/ udp 33", "video", "8208", "", "udp", "33", index: 0, input: "video 8208/ udp 33", groups: undefined]