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- #include "rtp-ext.h"
- #include <inttypes.h>
- #include <stdint.h>
- #include <stdlib.h>
- #include <string.h>
- #include <assert.h>
- #include <stdio.h>
-
- // https://webrtc.googlesource.com/src/+/refs/heads/main/docs/native-code/rtp-hdrext/abs-send-time
- /*
- Wire format: 1-byte extension, 3 bytes of data. total 4 bytes extra per packet (plus shared 4 bytes for all extensions present: 2 byte magic word 0xBEDE, 2 byte # of extensions). Will in practice replace the ¡°toffset¡± extension so we should see no long term increase in traffic as a result.
-
- Encoding: Timestamp is in seconds, 24 bit 6.18 fixed point, yielding 64s wraparound and 3.8us resolution (one increment for each 477 bytes going out on a 1Gbps interface).
-
- Relation to NTP timestamps: abs_send_time_24 = (ntp_timestamp_64 >> 14) & 0x00ffffff ; NTP timestamp is 32 bits for whole seconds, 32 bits fraction of second.
-
- SDP "a= name": "abs-send-time" ; this is also used in client/cloud signaling.
- */
-
- int rtp_ext_abs_send_time_parse(const uint8_t* data, int bytes, uint64_t *timestamp)
- {
- if (bytes < 3)
- return -1;
-
- *timestamp = ((uint64_t)data[0] << 16) | ((uint64_t)data[1] << 8) | data[2];
- *timestamp = (*timestamp * 1000000) >> 18;
- return 0;
- }
-
- int rtp_ext_abs_send_time_write(uint8_t* data, int bytes, uint64_t timestamp)
- {
- if (bytes < 3)
- return -1;
-
- timestamp = (timestamp << 18) / 1000000;
- data[0] = (uint8_t)(timestamp >> 16);
- data[1] = (uint8_t)(timestamp >> 8);
- data[2] = (uint8_t)(timestamp >> 0);
- return 3;
- }
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