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Re: [Linphone-developers] Question about speex

From: Vadim Lebedev
Subject: Re: [Linphone-developers] Question about speex
Date: Thu, 20 May 2010 18:47:40 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100423 Lightning/1.0b1 Thunderbird/3.0.4

I'm trying to guess here
But 50 seems to be packets per second

    maxbitrate/50  ==  bits per packet
    bitsperpacket/8 ==  bytes per packet

    IP header = 20 bytes, UDP header = 8 bytes, and RTP header = 12 bytes
    bytes per packet - 40 ==  speex payload bytes per packet

    speex payload bytes per packet * 50  =  speex payload bytes per second
   speex payload bytes per second * 8  == speex payload bits per second

Seems correct?


On 05/20/2010 03:19 PM, Sven Westergren wrote:

Can someone explain to me the reasoning behind this recalculation of bitrate in the speex plugin (msspeex.c)?

  /* convert from network bitrate to codec bitrate:*/
  /* ((nbr/(50*8)) -20-12-8)*50*8*/
  int cbr=(int)( ((((float)s->maxbitrate)/(50.0*8))-20-12-8)*50*8);

I have searched the speex manual but I can't grasp what is going on here.

Best regards
Sven Westergren
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