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rtpmap names and fmtp parameters

Match codecs by the rtpmap encoding name. The G.722 rtpmap clock stays 8000.

Learn in 5 minutes

  1. Match dynamic codecs by encoding name
  2. Recite the static payload types 0, 8, 9, and 18
  3. Keep the G.722 rtpmap clock at 8000

Visual

96 and 111 are both opus · study drawing · cyphermonkeylabs.com AliceCarrier INVITE 100 180 200

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Static types may omit rtpmap. Dynamic types are meaningless until rtpmap names them. G722/8000 is the required clock.

Worked example

Match opus on the name The offer says payload 96 opus. The answer says payload 111 opus. G722/8000 is on payload 9 on both sides.

  1. Press Negotiate.
  2. Find opus and compare the payload type numbers.
  3. Read the G722 clock on both sides.

Fault

One side offers a=rtpmap:9 G722/8000. The other side answers a=rtpmap:9 G722/16000 and no audio starts.

RFC 3551 sets the G.722 RTP clock to 8000 even though the audio sample rate is 16 kHz.

Quiz

Dynamic payload types are matched by


RFC 3551 assigns payload type 0 to


The rtpmap clock for G.722 is


A 20 ms G.722 timestamp increases by


a=fmtp applies to


Payload type 18 is


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