Re: Decoding raw AMR
Re: Decoding raw AMR
- Subject: Re: Decoding raw AMR
- From: James McCartney <email@hidden>
- Date: Tue, 30 Jan 2007 18:52:14 -0800
On Jan 30, 2007, at 9:46 AM, Martin Storsjö wrote:
On Mon, 29 Jan 2007, James McCartney wrote:
You should not attempt to use an AudioCodec directly but instead
use an AudioConverter. There are many subtle and sometimes counter-
intuitive details that are easy to get wrong when interacting with
various codecs directly.
The AMR codec requires a magic cookie in order to decode. If you
don't set the magic cookie on the AudioConverter, then the
AudioCodec will return kAudioCodecStateError.
A magic cookie is a string of bytes in some opaque codec-dependant
format which are used to configure the decoder.
Is there any documentation anywhere about what the magic cookie for
the AMR decoder should be? I've tried almost all imaginable
combinations of the actual file header and the first byte of the
packet (containing size information about the packet) or even the
whole packet, without success.
// Martin
I believe it is the 17 byte structure defined here:
3GPP2 File Formats for Multimedia Services
8.4.2.2 AMRSpecificBox field for AMRSampleEntry Box
where 'damr' is replaced by 'samr'
http://www.3gpp2.org/public_html/specs/C.S0050-0_v1.0_121503.pdf
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