From a35b6b0c4bcf93c7f261c6317a1a8e8eb141f33c Mon Sep 17 00:00:00 2001
From: ValdikSS <iam@valdikss.org.ru>
Date: Sun, 5 Apr 2026 19:58:00 +0300
Subject: [PATCH] bluez5: aac: use higher band limit for CBR mode

FDK-AAC encoder uses band pass filter, which is automatically
applied at all bitrates.
For CBR encoding mode, its values are as follows (for stereo):

* 0-12 kb/s:   5   kHz
* 12-20 kb/s:  6.4 kHz
* 20-28 kb/s:  9.6 kHz
* 40-56 kb/s:  13  kHz
* 56-72 kb/s:  16  kHz
* 72-576 kb/s: 17  kHz

VBR uses the following table (stereo):

* Mode 1: 13   kHz
* Mode 2: 13   kHz
* Mode 3: 15.7 kHz
* Mode 4: 16.5 kHz
* Mode 5: 19.3 kHz

17 kHz for CBR is a limiting value for high bitrate.

Assume >110 kbit/s as a "high bitrate" CBR and increase the
band pass cutout up to 19.3 kHz (as in mode 5 VBR).

Link: https://github.com/mstorsjo/fdk-aac/blob/d8e6b1a3aa606c450241632b64b703f21ea31ce3/libAACenc/src/bandwidth.cpp#L114-L160
---
 spa/plugins/bluez5/a2dp-codec-aac.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/spa/plugins/bluez5/a2dp-codec-aac.c b/spa/plugins/bluez5/a2dp-codec-aac.c
index 689e26ba6..c426dc1db 100644
--- a/spa/plugins/bluez5/a2dp-codec-aac.c
+++ b/spa/plugins/bluez5/a2dp-codec-aac.c
@@ -395,6 +395,15 @@ static void *codec_init(const struct media_codec *codec, uint32_t flags,
 	if (res != AACENC_OK)
 		goto error;
 
+	// Assume >110 kbit/s as a "high bitrate" CBR and increase the
+	// band pass cutout up to 19.3 kHz (as in mode 5 VBR).
+	if (!conf->vbr && this->cur_bitrate > 110000)  {
+		res = aacEncoder_SetParam(this->aacenc, AACENC_BANDWIDTH,
+				19293);
+		if (res != AACENC_OK)
+			goto error;
+	}
+
 	res = aacEncoder_SetParam(this->aacenc, AACENC_TRANSMUX, TT_MP4_LATM_MCP1);
 	if (res != AACENC_OK)
 		goto error;