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add some comments about packet structure

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fduncanh
2022-04-26 18:50:37 -04:00
parent 0464953c31
commit 1e9f6be43b
1 changed files with 21 additions and 1 deletions
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22
lib/raop_rtp.c
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@@ -466,7 +466,27 @@ raop_rtp_thread_udp(void *arg)
}
}
if (FD_ISSET(raop_rtp->dsock, &rfds)) {
/* rtp data packets: *
* packet[0] 0x80 (both AAC-ELD and ALAC) *
* packet[1] 0x80 = 96 *
* packet[2:3] (be short) seqnum *
* packet[4:7] (be int) rtp timestamp *
* packet[8:11] 0x00 0x00 0x00 0x00 *
* packet12:] encrypted audio payload */
/* consecutive AAC-ELD rtp timestamps differ by 480 *
* consecutive ALAC rtp timestamps differ by 352 *
* These are the respective spf (samples per frame) values *
* both have PCM uncompressed sampling rate = 441000 Hz */
/* clock time in microseconds advances at (rtp_timestamp * 1000000)/44100 between frames */
/* every AAC-ELD packet is sent three times: 0 0 1 0 1 2 1 2 3 2 3 4 ..... *
* (after decoding AAC-ELD into PCM, the sound frame is three times bigger) *
* ALAC packets are sent once only 0 1 2 3 4 5 ... */
if (FD_ISSET(raop_rtp->dsock, &rfds)) {
//logger_log(raop_rtp->logger, LOGGER_INFO, "Would have data packet in queue");
// Receiving audio data here
saddrlen = sizeof(saddr);