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add explanatory comment about when the SPS+PPS NAL is prepended to current NAL

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fduncanh
2022-05-05 12:11:29 -04:00
parent c1af5c8cc8
commit b41da5636b
1 changed files with 11 additions and 0 deletions
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11
lib/raop_rtp_mirror.c
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@@ -356,6 +356,17 @@ raop_rtp_mirror_thread(void *arg)
if (!raop_rtp_mirror->sps_pps_waiting && packet[5] != 0x00) {
logger_log(raop_rtp_mirror->logger, LOGGER_WARNING, "unexpected: packet[5] = %2.2x, but not preceded by SPS+PPS packet", packet[5]);
}
/* if a previous unencrypted packet contains an SPS (type 7) and PPS (type 8) NAL which has not
* yet been sent, it should be prepended to the current NAL. In this case packet[5] is usually
* 0x10; however, the M1 Macs have increased the h264 level, and now the encrypted packet after the
* unencrypted SPS+PPS packet may contain a SEI (type 6) NAL prepended to the next VCL NAL, with
* packet[5] = 0x00. Now the flag raop_rtp_mirror->sps_pps_waiting = true will signal that a
* previous packet contained a SPS NAL + a PPS NAL, that has not yet been sent. This will trigger
* prepending it to the current NAL, and the sps_pps_waiting flag will be set to false after
* it has been prepended. It is not clear if the case packet[5] = 0x10 will occur when
* raop_rtp_mirror->sps_pps = false, but if it does, the current code will prepend the stored
* PPS + NSPS NAL to the current encrypted NAL, and issue a warning message */
bool prepend_sps_pps = (raop_rtp_mirror->sps_pps_waiting || packet[5] != 0x00);
if (prepend_sps_pps) {
assert(raop_rtp_mirror->sps_pps);