Subject: [AVT] AMR Profile

From: B Prashanth <[email-masked]>
Date: Mon, 05 Jan 2004 19:05:31 +0530

Dear All,
Can anyone please tell me that if RTP stack is sending AMR speech data 
then does the encoded AMR payload, i.e. the AMR speech frame, contain 
the AMR frame header (specifying the Frame type) or Does the AMR speech 
frame contain just the raw, encoded speech data in the form of Class A, 
B and C bits?
Please note that the header being talked about here is the AMR speech 
frame's header and not the RTP's AMR profile header (Specified in RFC 3267).

-- 
Prashanth B.P.
Sr. Design Engr.
NeoMagic Design Center.
Polyplex Building, First Floor
B-37 Sector 1
Noida 
INDIA 201301
E-Mail:  [email-masked]
Tel:     +91-120-2536205/6  Extn:4103
Fax:     +91-120-2536207

NeoMagic Corporation, based in Santa Clara, California, provides Applications Processors to enable new generations of handheld systems, offering the lowest power, smallest form-factor, and best multimedia features and performance. The company has pioneered the integration of memory, complex logic, and analog circuits into single-chip solutions. 
URL: http://www.neomagic.com.
--

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
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---

From: Magnus Westerlund <[email-masked]>
Date: Mon, 12 Jan 2004 16:35:53 +0100

Hi,

When AMR is sent over RTP, the speech data in the payload format is as 
specified by RFC 3267. RFC 3267 gives the following information about 
how the speech data shall be arranged. From RFC 3267:

4.3.3. Speech Data

   Speech data of a payload contains one or more speech frames or
   comfort noise frames, as described in the ToC of the payload.

      Note, for ToC entries with FT=14 or 15, there will be no
      corresponding speech frame present in the speech data.

   Each speech frame represents 20 ms of speech encoded with the mode
   indicated in the FT field of the corresponding ToC entry.  The length
   of the speech frame is implicitly defined by the mode indicated in
   the FT field.  The order and numbering notation of the bits are as
   specified for Interface Format 1 (IF1) in [2] for AMR and [4] for
   AMR-WB.  As specified there, the bits of speech frames have been
   rearranged in order of decreasing sensitivity, while the bits of
   comfort noise frames are in the order produced by the encoder.  The
   resulting bit sequence for a frame of length K bits is denoted d(0),
   d(1), ..., d(K-1).

   [2]   3GPP TS 26.101, "AMR Speech Codec Frame Structure", version
         4.1.0 (2001-06), 3rd Generation Partnership Project (3GPP).

   [4]   3GPP TS 26.201 "AMR Wideband speech codec; Frame Structure",
         version 5.0.0 (2001-03), 3rd Generation Partnership Project
         (3GPP).

B Prashanth wrote:

> the AMR frame header (specifying the Frame type) or Does the AMR 
> speech frame contain just the raw, encoded speech data in the form of 
> Class A, B and C bits? 

The answer is that the speech frame does only contain the raw speech 
bits, denoted d(0)..d(K-1) as explained by Section 4.2 in TS 26.101. Not 
the the following IF1 fields: Frame Quality Indicator (1 bit), Mode 
Indication (3 bits), Mode Request (3 bits), and Codec CRC (8 bits). 
These fields are instead located in other fields in the RTP payload for 
AMR.

> frame's header and not the RTP's AMR profile header (Specified in RFC 

With AMR profile I assume that you are talking about the RTP payload 
format, not profile. A Profile is something else in RTP terms.

Do you think the quoted text is unclear and needs modification?

Cheers

Magnus Westerlund