[Live-devel] live 555 rtsp library for mplayer

[Ross Finlayson]

>When you stream audio over live-555's RTSP plugin  on mplayer, what 
>decides the
>audio data to be big endian vs little endian?

16-bit PCM audio data - when streamed using RTP using an 
IETF-standard RTP payload format - is *always* in Big Endian order 
(called "Network Byte Order" in the RFCs).  That's the standard[*].


>I am developing a server and I am
>specifying the format as 97 (dynamic format) with rtpmap being : 96 L16/8000
>for single channel, 16 bit/sample, 8 khz sample rate audio. But 
>mplayer somehow
>thinks audio data is in  big endian format and attaches a BE -> LE 
>conversion filter

It is correct; your server is not.  If your server's PCM data is 
originally in Little Endian order, then you need to insert a LE->BE 
filter in your server.  If you are using our libraries to build your 
server, then this involves just inserting a "EndianSwap16" filter 
object in front of your "SimpleRTPSink".  (If you are streaming from 
WAV audio files, then you could just use the 
"WAVAudioFileServerMediaSubsession" class, which does this for you. 
Note also our "LIVE555 Media Server", which can stream ".wav" audio 
files.)


[*] The reason for this is that IETF protocol standards began in an 
era when most computers on the Internet were Big Endian computers 
like Sun workstations (which originally used the Motorola 68xxx 
architecture).  Back then, computers that used the (Little Endian) 
Intel 8086 architecture were (generally speaking) too underpowered to 
be used as Internet nodes.  If we had known back then that the x86 
architecture would come to dominate the industry, then perhaps things 
would have been done differently....
-- 

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/