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The 4 octet meta data header contains information to be used by the decoder, Table below shows the format of the meta data. 

Octet

Description

0

Frame sequence number

1

Index into stepsize table for the start of the frame

2-3

Predicted value of first sample from the previous frame (little endian byte order)


Figure below shows the layout of the start of an ADPCM audio frame. 
Image Removed

Gliffy Diagram
macroIdad21b6d5-0c08-4004-90df-771a3095e7c9
nameAudio data
pagePin1


The sequence number shall be incremented for every audio frame encoded, even if the frame was discarded (i.e. in noisy environments). The sequence number shall wrap back to 0x00 after 0xFF. 
Both audio encoders shall use 4 bits per sample, and only one audio channel shall be sampled. The 4-bit samples are packed with the first sample in the four most significant bits and the second sample in the four least significant bits.

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