Internal filter-based structure

beginning at 0.9 wa2rtp tool have filter-based structure. This means than input signal passes these processing stages:

• Read from .wav file and encode with given codec and given codec options
• Process by filter 1 (for example, independent losses)
• Process by filter 2
• ... etc ...
• Write data to output .pcap file

Data from one stage to other is passed in the structure which represents RTP packet (see wr_rtp_packet_t). Each stage is processed by a filter. There is three types of filters:

1. Input filter. This filter cannot read data from other filters but can generate rtp packet "from itself". Currently implemented only one filter which reads data from .wav file
2. Intermediate filter. This filter is notified about input RTP data packet ("read data from stdin"), alter its data or meta-data (timestamp, etc) and calls the notification method which informs to its subscriber (or subscribers) - another filters, than new data packet is obtained.
3. Output filter. The one difference of this filter from previous variant is that this one never calls notification method.