The RTP header marker bit (M) is used to mark (M=1) the packages containing as their first frame the first speech frame after a comfort noise period in DTX operation. For all other packets the marker bit is set to zero (M=0).
The timestamp corresponds to the sampling instant of the first sample encoded for the first frame in the packet. A frame can be either encoded speech, comfort noise parameters, NO_DATA, or SPEECH_LOST (only for AMR-WB). The timestamp unit is in samples.
The duration of one speech frame is 20 ms and the sampling frequency is 8 kHz, corresponding to 160 encoded speech samples per frame for AMR and 16 kHz corresponding to 320 samples per frame in AMR-WB. Thus, the timestamp is increased by 160 for AMR and 320 for AMR-WB for each consecutive frame. All frames in a packet MUST be successive 20 ms frames except if interleaving is employed, then frames encapsulated into a payload MUST be picked
The payload MAY be padded using P bit in the RTP header.
references:
https://www.ietf.org/proceedings/51/I-D/draft-ietf-avt-rtp-amr-10.txt
The timestamp corresponds to the sampling instant of the first sample encoded for the first frame in the packet. A frame can be either encoded speech, comfort noise parameters, NO_DATA, or SPEECH_LOST (only for AMR-WB). The timestamp unit is in samples.
The duration of one speech frame is 20 ms and the sampling frequency is 8 kHz, corresponding to 160 encoded speech samples per frame for AMR and 16 kHz corresponding to 320 samples per frame in AMR-WB. Thus, the timestamp is increased by 160 for AMR and 320 for AMR-WB for each consecutive frame. All frames in a packet MUST be successive 20 ms frames except if interleaving is employed, then frames encapsulated into a payload MUST be picked
The payload MAY be padded using P bit in the RTP header.
references:
https://www.ietf.org/proceedings/51/I-D/draft-ietf-avt-rtp-amr-10.txt
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