Re: [MMUSIC] 4566bis - Attribute syntax: FEEDBACK REQUESTED
Christian Groves <Christian.Groves@nteczone.com> Wed, 13 August 2014 23:42 UTC
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Date: Thu, 14 Aug 2014 09:42:28 +1000
From: Christian Groves <Christian.Groves@nteczone.com>
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Subject: Re: [MMUSIC] 4566bis - Attribute syntax: FEEDBACK REQUESTED
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> Hello Paul, > > No worries. Please see below. > > I guess the question is whether you want to use the same syntax as > what has already been defined or whether you want to offer new syntax > imposing extra restrictions. No clear answer on that one. > > Regards, Christian > > On 13/08/2014 2:07 AM, Paul Kyzivat wrote: >> Christian, >> >> Thanks for being the first with feedback! Comments inline. >> >> Thanks, >> Paul >> >> On 8/11/14 10:23 PM, Christian Groves wrote: >>> Hello Paul, >>> >>> A few comments: >>> >>> a=rtpmap: >>> ----------- >>> a=rtpmap:<payload type> <encoding name>/<clock rate> [/<encoding >>> parameters>] >>> >>> Syntax: >>> >>> rtpmap-value = payload-type SP encoding-name "/" clock-rate >>> [ "/" encoding-params ] >>> payload-type = integer >>> encoding-name = token ; ? >>> clock-rate = integer >>> ; do we want to define a limited range for this? >>> encoding-params = token ; ? >>> ; 4566 is vague about what this can be. The only example is >>> an integer. >>> ; nor is it clear how multiple params would be encoded >>> >>> 1) Would you be better sticking to "fmt" for the payload-type as >>> that is >>> what is already used in the 4566 syntax? i.e. >>> >>> media-field = %x6d "=" media SP port ["/" integer] >>> SP proto 1*(SP fmt) CRLF >> >> rtpmap is only used for protos from the rtp family, where the fmts >> are integers. So I don't think we should be more general than that. >> >> IIUC, the pt is carried in a fixed size field in RTP, so we might >> want to limit the range to what that allows. > [CNG] I was thinking also of consistency. Your a=ftmp syntax uses > "fmt" for the same field. > >> >>> 2) encoding-name: According to RFC4855 the media subtype >>> (encoding-name) >>> is encoding according to RFC2045 i.e. subtype := extension-token / >>> iana-token. If you want to get more precise you could refer to RFC4288 >>> cl. 4.2. >> >> Thanks for the research! >> >> Section 3 of RFC4855 (Media Type Registration of RTP Payload Formats) >> says that encoding-name is equivalent to <subtype> defined in RFC2045. >> This ultimately seems to be <token> defined in that rfc. And that is: >> >> token := 1*<any (US-ASCII) CHAR except SPACE, CTLs, >> or tspecials> >> >> tspecials := "(" / ")" / "<" / ">" / "@" / >> "," / ";" / ":" / "\" / <"> >> "/" / "[" / "]" / "?" / "=" >> >> This is hard to reference directly. But if you study it, it is >> equivalent to the RFC4566 definition of <token>. >> >> RFC4855 also refers to RFC4288 (Media Type Specifications and >> Registration Procedures) as the basic mechanism for registering >> encoding-names as mime subtypes. The definition there is more >> restrictive: >> >> reg-name = 1*127reg-name-chars >> reg-name-chars = ALPHA / DIGIT / "!" / >> "#" / "$" / "&" / "." / >> "+" / "-" / "^" / "_" >> >> So I think we have to possibilities: >> >> encoding-name = token >> encoding-name = subtype-name >> ; as defined in RFC4288 >> >> Since the names must be registered, I think we are safe in going the >> easy way and just using <token>. > [CNG] I think it would be better to use the restrictive syntax. If the > IANA procedures say one thing and the syntax another, its open to > heartache at some point. Token doesn't equal reg-name. > >> >>> 3) RFC4855 last paragraph cl.3 indicates case insensitivity. >> >> OK. That has to be specified in semantics, not syntax. > [CNG] Yes >> >>> 4) For the Clock Rate and Encoding parameters RFC4288 cl.4.3 indicates >>> requirements for the names / values. >> >> That gives the generic syntax for all names and values. But these >> parameters are intended to be numeric. Do we really want to use a >> syntax that allows them to be non-numeric? > [CNG] I agree clock rate is meant to be numeric. The general encoding > parameters could basically be anything. >> >>> a=sdplang & a=lang >>> -------------------- >>> 1) Do you have the right reference in: >>> sdplang-value = Language-Tag ; defined in RFC5234 >>> >>> should this be RFC5646? >> >> Yes. That is where I was looking. I just typed the wrong thing. >> >> Examining that definition further, it is a proper subset of SDP >> <token>. We may prefer to just use that, since the registries will >> enforce the subsetting for valid tags. > [CNG] Even though it may ultimately be a token I think its worth > referencing the RFC5646 syntax. At least people then are forced to try > and understand it. If its just left as TOKEN it could be anything. >> >> >>> a=framerate >>> ----------- >>> 1) positive-real-number = (integer / "0") [ "." *integer ] is the * >>> before the last integer needed? It would make sense if integer was >>> digit. >> >> Oops. What I meant was: >> >> positive-real-number = (integer / "0") [ "." [integer] ] >> >> Or we could be more restrictive, as: >> >> positive-real-number = (integer / "0") [ "." integer ] > [CNG] I can't see why someone would use "1." which the first option > would allow. I'd prefer the restrictive option however I can see the > argument that given the number of implementations out there it may pay > to be more lax. >> >> >>> a=quality >>> --------- >>> 1) If the value range is 0 to 10. Should you limit the values in the >>> syntax also? i.e. just using "integer" would allow sending "11". >> >> I saw that. But it says *for video* the range is 0 to 10. But AFAIK >> this isn't restricted to use for other types of media. It just >> doesn't define what it means for other media. > [CNG] Perhaps it might be worth proposing that this is only for video > and see if anybody screams? If someone is using a value quality=150 > for audio. What does that mean? Outside of some proprietary usage it > doesn't seem particularly interoperable. >> >> Thanks, >> Paul >>
- [MMUSIC] 4566bis - Attribute syntax: FEEDBACK REQ… Paul Kyzivat
- Re: [MMUSIC] 4566bis - Attribute syntax: FEEDBACK… Paul Kyzivat
- Re: [MMUSIC] 4566bis - Attribute syntax: FEEDBACK… Fredrik Bergholtz
- Re: [MMUSIC] 4566bis - Attribute syntax: FEEDBACK… Paul Kyzivat
- [MMUSIC] 4566bis - Attribute syntax: FEEDBACK REQ… Fredrik Bergholtz
- Re: [MMUSIC] 4566bis - Attribute syntax: FEEDBACK… Christian Groves
- Re: [MMUSIC] 4566bis - Attribute syntax: FEEDBACK… Paul Kyzivat