Subject: [media-types] Registration of audio/aptx

From: "Ali C. Begen (abegen)" <[email-masked]>
Date: Sat, 19 Oct 2013 05:27:12 +0000

Hello, 

The following draft is requesting to register a new media subtype (Section 6.1). Your review is appreciated. 
https://datatracker.ietf.org/doc/draft-ietf-payload-rtp-aptx/?include_text=1

Below is the text.

Thanks,
-acbegen
Payload WG Co-Chair

Registration of media subtype audio/aptx.

     MIME media type name: audio

     MIME subtype name: aptx

     Required parameters:

        rate:
        RTP timestamp clock rate, which is equal to the sampling rate
        in Hz.  -- RECOMMENDED values for rate are 8000, 11025, 16000, 
        22050, 24000, 32000, 44100 and 48000 samples per second. Other 
        values are permissible.

        channels:
        The number of logical audio channels that are present in the  
        audio stream.

        variant:
        The variant of apt-X (i.e.  Standard or Enhanced) that is being
        used.  The following variants can be signalled:

           variant=standard
           variant=enhanced

        bitresolution:
        The number of bits used by the algorithm to encode 4 PCM
        samples.  This value MAY only be set to 16 for Standard apt-X
        and 16 or 24 for Enhanced apt-X.

     Optional parameters:

        ptime:
        The recommended length of time (in milliseconds) represented by
        the media in a packet.  Defaults to 4 ms. See Section 6 of 
        [RFC4566].

        maxptime:
        The maximum length of time (in milliseconds) that can be
        encapsulated in a packet.  See Section 6 of [RFC4566].

        stereo-channel-pairs:
        Defines audio channels that are stereo paired in the stream. 
        See Section 3.  Each pair of audio channels is defined as two 
        comma-separated values that correspond to channel numbers in 
        the range 1..channels.  Each stereo channel pair is preceded 
        by a '{', and followed by a '}'.  Pairs of audio channels are 
        separated by a comma.  A channel MUST NOT be paired with more
        than one other channel.  Absence of this parameter signals that
        each channel has been independently encoded.

        embedded-autosync-channels:
        Defines channels that carry embedded autosync.  embedded-
        autosync-channels is defined as a list of comma-separated 
        values that correspond to channel numbers in the range 1..
        channels.  When a channel is stereo paired, embedded autosync
        is shared across channels in the pair. Only the first channel 
        as defined in stereo-channel-pairs MUST be specified in the 
        embedded-autosync-channels list.

        embedded-aux-channels: 
        Defines channels that carry embedded auxiliary data.  embedded-
        aux-channel is defined as a list of comma-separated values 
        that correspond to channel numbers in the range 1..channels.
        When a channel is stereo paired, embedded auxiliary data is 
        shared across channels in the pair. Only the second channel as 
        defined in stereo-channel-pairs MUST be specified in the
        embedded-autosync-channels list.

     Encoding considerations: This type is only defined for transfer
     via RTP [RFC3550].

     Security considerations: See Section 5 of [RFC4855] and Section 4
     of [RFC4856].

     Interoperability considerations: none

     Published specification: RFC XXXX

     Applications which use this media type: Audio streaming

     Additional information: none

     Person & email address to contact for further information: John 
     Lindsay email:[email-masked]

     Intended usage: COMMON

     Author/Change controller: John Lindsay

---

From: Bjoern Hoehrmann <[email-masked]>
Date: Sat, 19 Oct 2013 12:17:40 +0200

>     MIME media type name: audio

This is based on an obsolete version of the registration template. The
current one http://tools.ietf.org/html/rfc6838#section-5.6 is slightly
different, for instance, this field should be `Type name:`.

>     MIME subtype name: aptx

(It seems a bit odd to call the codec "apt-X" but the type "aptx".)

>        the media in a packet.  Defaults to 4 ms. See Section 6 of 

(It might be better to say "Defaults to 4 (milliseconds)", otherwise
some might be confused whether the `ms` is part of the value.)

>        each channel has been independently encoded.

If the value includes characters like `{` then in protocols like HTTP
the value would have to be enclosed in double quotes since `{` is not
allowed as a bare token in that protocol. The situation may be similar
in RTP, and if so, that's not sufficiently clear from the text above.
The same goes for some other parameters and other characters like `,`.

>        embedded-autosync-channels list.

This should be rephrased to avoid combining "MUST" and "only"; it is
not clear whether specifying more than the first channel is optional
or forbidden. Same for the `embedded-aux-channels` parameter.

>     Encoding considerations: This type is only defined for transfer

Per http://tools.ietf.org/html/rfc6838#section-4.8 this should be one
of the values defined in that section, probably `framed`. That it is
only defined for RTP should go into the `Restrictions on usage:` field.

>     Lindsay email:[email-masked]

This would be better as `John Lindsay <[email-masked]>`.

>     Author/Change controller: John Lindsay

Since this is a registration in the standards tree, assigning change
control to an individual requires some justification, I think.
-- 
Björn Höhrmann · mailto:[email-masked] · http://bjoern.hoehrmann.de
Am Badedeich 7 · Telefon: +49(0)160/4415681 · http://www.bjoernsworld.de
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