diff options
Diffstat (limited to 'main/stream_server.c')
| -rw-r--r-- | main/stream_server.c | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/main/stream_server.c b/main/stream_server.c index c417e4a..1321f22 100644 --- a/main/stream_server.c +++ b/main/stream_server.c @@ -18,6 +18,29 @@ static const char *TAG = "stream"; +// Why TCP and not UDP. +// +// JPEGs at panel-native q:v 1 are ~180 KB → ~123 IP datagrams at 1500 +// MTU. On hardwired Gigabit LAN with a single managed switch, fabric +// loss is < 1e-9/packet, so per-frame corruption is ≈1.2e-7 (~1 bad +// frame every 95 days at 30 fps). UDP's theoretical wins don't apply +// to this deployment: +// +// - Nagle/SACK/window-scaling overhead: socket.write p50 < 1ms in +// steady state (see Scrypted-side log). TCP_NODELAY is on. No +// per-frame ACK round-trip exists in either direction. +// - "Latest wins" semantics: implemented for free above via the +// FIONREAD check below. UDP would have to reassemble fragments +// first before deciding to skip, defeating the latency win. +// +// UDP's costs would be real: 200-400 LOC of app-layer fragmentation +// + reassembly + partial-frame timeout, loss of `nc localhost 81 | +// xxd` for debug, and the FIONREAD-skip trick stops working because +// UDP recvmsg counts fragments not whole messages. +// +// Revisit only if a Wi-Fi-only variant ships (loss rate 1e-3..1e-5 +// would make TCP retransmits painful enough to consider the rewrite). + #define HEADER_V0_BYTES 8 // legacy: jpeg_len + seq #define HEADER_V1_BYTES 16 // current: magic + jpeg_len + seq + event_us_low #define HEADER_BYTES HEADER_V0_BYTES // used for FIONREAD threshold — |