From 1d7e89e06935405b08f47663a4de70319807686e Mon Sep 17 00:00:00 2001
From: Pauli Virtanen <pav@iki.fi>
Date: Tue, 23 Dec 2025 20:28:40 +0200
Subject: [PATCH] bluez5: media-source: improve handling of underrun with PLC

When PLC data was produced due to underrun and decode buffer has reached
target level, drop received audio if we already did PLC for that packet.
It's better to lose some packets than having to resync latency.

When about to underrun when PLC is active, update rate matching before
filling up buffer, so that rate slows down and we do not get stuck in a
continuous underrun where PLC fills data and we drop received packets.
---
 spa/plugins/bluez5/media-source.c | 34 ++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/spa/plugins/bluez5/media-source.c b/spa/plugins/bluez5/media-source.c
index ebd6c92a7..14896d6b3 100644
--- a/spa/plugins/bluez5/media-source.c
+++ b/spa/plugins/bluez5/media-source.c
@@ -573,6 +573,7 @@ static int produce_plc_data(struct impl *this)
 static int32_t decode_data(struct impl *this, uint8_t *src, uint32_t src_size,
 		uint8_t *dst, uint32_t dst_size, uint32_t *dst_out, int pkt_seqnum)
 {
+	struct port *port = &this->port;
 	ssize_t processed;
 	size_t written, avail;
 	size_t src_avail = src_size;
@@ -606,14 +607,19 @@ static int32_t decode_data(struct impl *this, uint8_t *src, uint32_t src_size,
 			lost = 0;
 		}
 
-		if (lost >= this->plc_packets) {
+		if (lost >= this->plc_packets)
 			lost -= this->plc_packets;
-		} else {
-			/* We already produced PLC audio for this packet.  However, this
-			 * only occurs if we are underflowing, so we should retain this
-			 * packet regardless and let rate matching take care of it.
+		else
+			this->plc_packets -= lost;
+
+		if (this->plc_packets &&
+				port->buffer.level > spa_bt_decode_buffer_get_target_latency(&port->buffer)) {
+			/* We already produced PLC audio for this packet, and have enough
+			 * data, so drop the packet.
 			 */
-			lost = 0;
+			spa_log_debug(this->log, "%p: PLC drop %u sn:%u", this, this->plc_packets, seqnum);
+			this->plc_packets--;
+			return 0;
 		}
 
 		/* Pad with PLC audio for any missing packets */
@@ -1750,7 +1756,8 @@ static uint32_t get_samples(struct impl *this, int64_t *duration_ns)
 		rate_denom = port->current_format.info.raw.rate;
 	}
 
-	*duration_ns = duration * SPA_NSEC_PER_SEC / rate_denom;
+	if (duration_ns)
+		*duration_ns = duration * SPA_NSEC_PER_SEC / rate_denom;
 
 	if (SPA_LIKELY(port->rate_match) && this->resampling) {
 		samples = port->rate_match->size;
@@ -1805,16 +1812,19 @@ static void process_buffering(struct impl *this)
 	if (samples > this->quantum_limit)
 		return;
 
-	/* Produce PLC data if possible to avoid underrun */
+	spa_bt_decode_buffer_process(&port->buffer, samples, duration_ns);
+
+	/* Produce PLC data if possible to avoid underrun instead of buffering pause */
 	while (spa_bt_decode_buffer_get_size(&port->buffer) < data_size) {
 		if (produce_plc_data(this) <= 0)
 			break;
 		plc = true;
 	}
-	if (plc)
-		spa_bt_decode_buffer_recover(&port->buffer);
-
-	spa_bt_decode_buffer_process(&port->buffer, samples, duration_ns);
+	if (plc) {
+		port->buffer.buffering = false;
+		if (port->buffer.corr > 1.0)
+			spa_bt_decode_buffer_recover(&port->buffer);
+	}
 
 	setup_matching(this);