Codec framework enhancement: Interaction with SDP

[nanang]

1. Type of attributes
   • ptime. Some codecs want to signal ptime, but this may not the best mechanism to use since ptime applies to the whole stream.
   • maxptime. Currently is signaled by AMR. Example:

     a=maxptime:20
     

   • fmtp. Examples:

     a=fmtp:18 annexb=no
     a=fmtp:97 mode-set=0,2,5,7; mode-change-period=2; mode-change-neighbor=1
     a=fmtp:101 bitrate=24000
     

2. Encoding offer:
   • initial offer should encode codec settings/preference
   • subsequent offer should encode the setting of current codec instance (?)

3. Feature/format negotiation in negotiator. Example:
   • fmtp: to negotiate bitrate for some codecs (e.g. G.722.1, SIREN, etc):

     a=fmtp:101 bitrate=24000"
     

4. Processing answer

[nanang]

In r2236:

• Added "dec_fmtp" and "enc_fmtp" fields to pjmedia_codec_param.setting.
• Codec factory puts its default parameters in "dec_fmtp" field.
• pjmedia_stream_info_from_sdp() puts the "fmtp" attribute in SDP to pjmedia_codec_param.
• Special treatment for fmtp "bitrate" parameter (of G722.1) during SDP negotiation
• Added maxptime field in stream_info.
• Replaced iLBC's fmtp "mode" implementation to use general fmtp mechanism.
• Added some test scripts for G722.1 bitrate negotiation.

[bennylp]

Done, closing the ticket.