Regarding recreation of pjmedia_ports when reinvite causes change in stream port characteristics

[MayamaTakeshi]

If the following stream port characteristics

• sampling_rate (PJMEDIA_PIA_SRATE)
• channel_count (PJMEDIA_PIA_CCNT)
• samples_per_frame (PJMEDIA_PIA_SPF)
• bits_per_sample (PJMEDIA_PIA_BITS)
  change in a reinvite, we recreate the AudioEndpoint conf (Create conf per AudioEndpoint #74) and add the new stream port and new dtmfdet port to it.
  However the other ports are not recreated/added.
  Let's consider if this would be possible:
• wav_player: we might need to do this:
  • add a function to permit to check the number of samples that were played so far (well we might get stats from some pjmedia function)
  • recreate the port and seek to the number of samples so that we can continue playing from it
• wav_writer:
  • when the port is destroyed, ensure the wav file is closed
  • the port create function should be modified with bool parameter 'append' which would indicate to open an existing wav file and append to it.
  • recreate the port with parameter 'append' set to true
• tonegen (inband dtmf generation):
  • the port needs to provide a function to check the pending digits to be sent
  • when recreating the port, immediately add the pending digits to it (obs: this would be susceptible to a gitch so we might need to indicate if the first digit must be immediately generated if its output was not complete in the previous port
• fax: this might not be doable as we would be in the middle of fax communication and we cannot open a tiff file for seek-read or append like we would do with wav_player/wav_writer
• flite: similar to wav_player (seek to number of samples transmitted so far)
• pocketsphinx (future):
  • need to have a function to permit to flush partial transcripts. But if there is not, just recreate the port

In all cases, a resample_port might need to be added.