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SDP codec manipulation

New functions have been added for SDP codec manipulation in the textops module:

• codec_exists(name[,clock]); - tests if a codec exists
• codec_delete(name[,clock]); - deletes a codec
• codec_move_up(name[,clock]); - moves a codec to the front of the priority list
• codec_move_down(name[,clock]); - move a codec to the back of the priority list

Each of them can take a codec name and an optional clock parameter. If the clock is unspecified all of the codecs with that name will match.

All of the methods will act on all streams from all sessions inside the SDP.

You can use these methods one after another to get a desired effect.

E.g. To make GSM the least prefered codec but GSM/8000 the most prefered of all GSM codecs use:

codec_move_up("GSM","8000");
codec_move_down("GSM");

Once a codec was deleted it will not be detected by codec_exists().