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A question about codec in JMF  RSS feed

walter wang
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Dear All I had a question about codec
I check about codec
it said ulaw is a kind of codec(compression rate is 50%)
but i am more confused after seeing some implemation code
one example is encoding captured audio data
it will encode captured audio data in the IMA4 format(codec) before saving it into
a file(*.wav)
so i guess if you didnot explicit set output media file's codec format
before saveing data into output media file, then this file will have
no codec format (not compressed), you will store raw data into media file.
Is it correct?
another example is sending out a file
sending out a media file( which is *.avi file)
firstly setup RTP configuration and create configuration for flows(setting up codec)

SenderCofig[]flows={ new SenderConfig(config1, new AudioFormat(AudioFormat.ULAW_RTP)),//setting up codec
new SenderConfig(config2, new VideoFormat(VideoFormat.JPEG_RTP)) //setting up codec
then you send out
But media file, which is sent, is *.avi file
if this *.avi flie had its' own codec format already
during sending , if you setting up codec again (in this case AudioFormat.ULAW_RTP)
will this coverting cause problem?
I want to know if each media file (eg *.avi, *.au, *.jpeg)has it's own codec? ,doest those media files
support storing in raw data format?
I mean could we store raw data(without codecing them) into media file(*.avi,*.au, *.jpeg)?
or when we store data into mediafile, we must codec (compress)them before saving them into media files?
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