[CELT-dev] celtclient 64kbps more than expected

Jean-Marc Valin jean-marc.valin at usherbrooke.ca
Thu Jun 4 04:26:06 PDT 2009

Hi Paul,

I think the issue you're seeing here is simply the overhead of the IP
(20 bytes) and UDP (8 bytes) headers (plus our 8-byte timestamp/header).
With a frame size of 256 at 48 kHz, you send 188 packets/sec, which
means about 45 kbit/s of header overhead. Depending on how you're
measuring, you may be seeing the Ethernet overhead of something like
that. All I can assure you is that when you ask CELT for 43 bytes, this
is *exactly* what you receive. Does that explain the numbers you have?



Paul Sykes a écrit :
> Hi,
> The default settings for celtclient are:-
> Sampling rate 48000
> Frame size 256
> Packet size 43
> According to my calculations this should give a bitrate of 64kbit/sec +
> a little extra for the 32bit time stamp and 4 null byte pseudo header.
> Using vnstat I was very surprised to see that it was reporting a bitrate
> usage of around 16kbyte/sec  which is 128kbit/sec, double what I was
> expecting.
> I then changed packet size to 86 which I expected should give a bitrate
> of 128kbit/sec, vnstat said I was using 24kbyte/sec which is 192kbit/sec
> I then changed packet size to 128, I expected to see a bitrate of
> 192kbit/sec, vnstat gave me a bitrate of 32kbyte/sec which is
> 256kbit/sec
> Therefore all measurements were 64kbit/sec greater than I anticipated,
> can somebody tell me why, or I have got something wrong here?
> thank you,
> Paul.
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