Subject: RTSP: range-header support; smpte

From: [email-masked]
Date: Wed, 19 Nov 1997 00:29:40 -0500 (EST)

range-header support
--------------------

why is range header support required now for minimal clients/servers ? i sent
mail to the list a couple of months ago, and was told that range-header
support wasn't required.

a minimal server simply takes a complete audio/video file, and sends it out
on the net. the capability of extracting sub-clips, while very useful,
requires more complex code in the server - i guess in the case of
differential compressions schemes such as MPEG, it may even require
re-compression, if you end up addressing a differential frame in the range
request.

smpte
------

there are more smpte codes than the smpte-30-drop supported by rtsp.
"european" video uses smpte-25, for example. i guess a sentence on how these
should be handled within rtsp would be helpful, i.e. how do you map from
smpte-30-drop onto other smpte codes.

---

From: Rob Lanphier <[email-masked]>
Date: Wed, 19 Nov 1997 23:42:37 -0800

>mail to the list a couple of months ago, and was told that range-header

Because we were silly :)  I'm assuming it's section D.1.1 that's the
problem.  I'll change both to read:

*  To support on-demand, seekable playback of media streams, the server MUST 
                         ^^^^^^^^
   be able to do the following:

....

>smpte-30-drop onto other smpte codes.

Hmmm, that is a rather US-centric blunder.  

Well, I would say that smpte-25 would need to be it's own timestamp format,
and that each other one would have it's own mapping.  I'm not sure where
our copy of the SMPTE spec ended up, so I'll have to hunt around for it.  

Perhaps we could include it thusly:

The default smpte format is``SMPTE 30 drop'' format, with frame rate is
29.97 frames per second.  Other SMPTE codes MAY be supported (such as
"SMPTE 25") through the use of alternative use of "smpte time".   For the
``frames'' field 
in the time value can assume the values 0 through 29. 
The difference between 30 and 29.97 frames per second is handled by
dropping the first two frame indices (values 00 and 01) of every minute,
except every tenth minute.  If the frame value is zero, it may be
omitted.  Subframes are measured in one-hundredth of a frame.

  smpte-type = "smpte" | "smpte-30-drop" | "smpte-25"
                                            ; Other timecodes may be added
  smpte-range = smpte-type "=" smpte-time "-" [ smpte-time ]
  smpte-time = 1*2DIGIT ":" 1*2DIGIT ":" 1*2DIGIT [ ":" 1*2DIGIT ] 
               [ "." 1*2DIGIT]

Rob
---
Rob Lanphier ([email-masked])    Voice: (206)674-2322   Fax: (206)674-2699
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