GSM AMR output

Greetings.

The GSM AMR output has only 0xff81 and 0x007f only. Why is it not that
one can compress the stream further that sends the number of ff81 and
number of 7f in the encoder output stream.
as in:
ff81 ff81 007f 007f 007f 007f 007f 007f 007f
can be: ff81 02 007f 07 ... or some other flag to represent ff81 and
007f
One can compress the output further remarkably and will require to put
a small "stream regenerator".
I have not seen the GSM AMR output with any other content apart from
the above two values. Why is it so ?

Thanks,
Akshay

Self correction on realisation. !!

there are 253 bytes ouput of ff81/007f hence to achieve the 12.65kbps
link you send the sign bits to the other end. even the flag/count pain
is not required.

Am I correct here.

Thanks,
Akshay

Akshay Mishra wrote:
> Greetings.
>
> The GSM AMR output has only 0xff81 and 0x007f only. Why is it not that
> one can compress the stream further that sends the number of ff81 and
> number of 7f in the encoder output stream.
> as in:
> ff81 ff81 007f 007f 007f 007f 007f 007f 007f
> can be: ff81 02 007f 07 ... or some other flag to represent ff81 and
> 007f
> One can compress the output further remarkably and will require to put
> a small "stream regenerator".
> I have not seen the GSM AMR output with any other content apart from
> the above two values. Why is it so ?
> 
> Thanks,
> Akshay