Hi David,
On 02-11-11 21:02, David Rowe wrote:
>> E.g. I looked in the source-code of c2enc.c and c2dec.c, but did not
>> find any commands to -say- configure the bitrate of the encoder.
> Only one bit rate is currently supported. Actually the work I am doing
> to more efficiently encode LSPs suggests we can maintain roughly the
> same quality down to say 1400 bit/s. So there may not be a need for
> different bit rates yet, e.g. 2400 bit/s won't sound better than 1400
> bit/s.
OK, I understand.
But I try to look at it from application point of view.
Say you write an application that encodes 20 ms of voice, and stuffs it
into a (after adding FEC and other data) for transmission over some
radio-medium (a VHF gmsk channel, a HF COFDM channel, ...)
It would be usefull for meto know beforehand how large the encoded audio
will be, so I know if it will fit into the frame or not. :-)
At least, I would like to be able to control the encoding process in
some way (like to set a maximum bitrate).
I see that the new lower bitrate versions use differencial encoding
("coding frame-frame differences").
I guess this means that, if the first frame of a "group" is lost, the
content of all other frames becomes irrelevant and will have to be ignored.
That's OK in certain situations (like a UDP/RTP stream over the
internet), but not good in other situations (e.g. over a radio-channel
with a bad S/N ratio).
In the latter case, an application might prefer an encoding-sceme that
does not do differencial encoding (which does mean, higher bitrate) but
not transmit any data alongside in voice in the stream.
So, as I see it, it does make sence to let applications have some kind
of control over the encoding process. This would (IMHO) require some
kind of standardised API.
> - David
73
Kristoff - ON1ARF
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