Media Types in 3GPP Timed text draft (was: RE: [AVT] RTP andMediaTypes)

Dave Singer singer at
Tue Sep 7 15:37:41 CEST 2004

At 1:25 PM +0100 9/7/04, Colin Perkins wrote:
>On 7 Sep 2004, at 12:56, Jose Rey wrote:
>>>-----Original Message-----
>>>From: Colin Perkins [mailto:csp at]
>>>Sent: Tuesday, September 07, 2004 12:03 PM
>>>To: Jose Rey
>>>Cc: IETF AVT WG; Dave Singer; Magnus Westerlund; IETF-Types
>>>Subject: Re: Media Types in 3GPP Timed text draft (was: RE: [AVT] 
>>>RTP andMediaTypes)
>>>On 17 Aug 2004, at 14:42, Jose Rey wrote:
>>>>Dave and I have been discussing this offline and come to the following
>>>>1.- it is not envisioned that the 3GPP Timed Text payload format will
>>>>used for applications such as instant messaging or text conversation,
>>>>which do not precise of text decoration for working properly, since
>>>>there are other more appropriate media types covering these usages,
>>>>like text/t140. Hence,  video/ is enough.
>>>I agree that this is not likely to be used for instant messaging or
>>>text conversation, although I don't understand why that would be
>>>Is this fundamentally text or a video codec? If it's a video
>>>codec, it should be under "video/", otherwise under "text/".
>>I think it is a video codec, since without the video capabilities
>>(modifiers) it would just provide the same services as , e.g.,
>>conversational text=just plain timed text, for which it is not 
>>thought to be used.
>There are other text formats that include formatting modifiers, for 
>example "text/html". I don't understand why their presence would 
>make this a video format.

But text/html is not only rendering text, it is expressed in text. 
3GPP renders text, but it is expressed in binary.

>>>>2.- we are not clear on what exactly means to "relax rules for media
>>>>registration under text/".  I.e. is text/t140 an example of these
>>>>"relaxed" rules or does it comply with the traditional rules as per
>>>>rfc 2046?  Does the relaxed rules just mean that besides text also
>>>>payload headers of that media type are udnerstood?
>>>My understanding is that the new rules are intended to allow formats
>>>such as 3GPP timed text to be registered under the text top-level media
>>>type, if appropriate, provided their domain of applicability is clearly
>>>specified (e.g. the domain of applicability might be that the type is
>>>defined for transfer via RTP only).
>>The MIME subtype /3gpp-tt cannot be used for HTML download since for that
>>purpose a 3gp file and therefore the video/3gp MIME type is used.  So I
>>think this is indeed restricted to RTP.  However,  what is the gain 
>>of doing that?
>My point was that, since this is restricted to transport via RTP, it 
>can be registered under the "text" top-level media type.
>>Given the answer to the first question I think registering under
>>text/ would not be of any use?
>Why not? It would seem to be the natural home for a timed text format.

David Singer
Apple Computer/QuickTime

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