[Speex-dev] Re: Sending speex over a network

[Jim Crichton]

The usual answer to your question is "Read the manual", but you are 
obviously trying.

Speex encodes 20 ms frames of audio.  This translates into 160 for Speex 
narrowband mode (8kHz speech samples), 320 for wideband mode (16kHz speech 
samples), and 640 for ultra-wideband mode (32kHz speech samples).   You must 
use the proper value for your mode, or you will get garbled speech.  The 
encoded data rate is set with the Quality parameter, and that is probably 
what you want to be experimenting with.  The comment in sampleenc.c:

/*The frame size in hardcoded for this sample code but it doesn't have to 
be*/

is a little misleading.  What it really means is that your code can make the 
mode selectable between NB, WB, and UWB, as it is in speexenc.c.  You might 
want to look at testenc.c and testenc_wb.c in the libspeex directory.  These 
files just loop the encoder to the decoder, but they still produce the 
encoded file.

Of course, if you are sending Speex over a network, you are free to put 
multiple Speex frames into a packet, but this is done outside of the codec. 
The IP/UDP/RTP overhead of 40 bytes per packet yields a depressing 16kbps at 
50 packets/second.

- Jim

----- Original Message ----- 
From: "Jean-Marc Valin" <jean-marc.valin at usherbrooke.ca>
To: "Nichole Arel" <nichole.arel at gmail.com>
Cc: <speex-dev at xiph.org>
Sent: Wednesday, May 02, 2007 8:57 PM
Subject: Re: [Speex-dev] Re: Sending speex over a network


>> In sampleenc.c and sampledec.c, if I change the FRAME_SIZE to any other
>> value, I get very garbled speech. Can anyone tell me if I need to set
>> something else if I would like to change the frame size ?
>
> No, you need to write another codec :-)
>
> Jean-Marc
>
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