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kvm
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refactor: Simplify audio implementation 

Remove dynamic gain code and rely on Opus encoder quality improvements:
- Increase Opus complexity from 2 to 5 for better quality
- Change bandwidth from FULLBAND (20kHz) to SUPERWIDEBAND (16kHz) for better quality at 128kbps
- Disable FEC to allocate all bits to audio quality
- Increase ALSA buffer from 40ms to 80ms for stability

The dynamic gain code was adding complexity without solving the underlying
issue: TC358743 HDMI chip captures digital audio at whatever volume the
source outputs. Users should adjust volume at the source or in their browser.
This commit is contained in:
Alex P 2025-10-07 00:25:45 +03:00
parent 04dd37f58f
commit 19fe908426
2 changed files with 5 additions and 71 deletions
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2
audio.go
View File

@ -80,7 +80,7 @@ func startAudioSubprocesses() error {
[]string{
"ALSA_CAPTURE_DEVICE=" + alsaDevice,
"OPUS_BITRATE=128000",
"OPUS_COMPLEXITY=2",
"OPUS_COMPLEXITY=5",
},
)

74
internal/audio/c/audio.c
View File

@ -55,14 +55,14 @@ static uint8_t channels = 2;
static uint16_t frame_size = 960; // 20ms frames at 48kHz
static uint32_t opus_bitrate = 128000;
static uint8_t opus_complexity = 2;
static uint8_t opus_complexity = 5; // Higher complexity for better quality on RV1106
static uint16_t max_packet_size = 1500;
// Opus encoder constants (hardcoded for production)
#define OPUS_VBR 1 // VBR enabled
#define OPUS_VBR_CONSTRAINT 0 // Unconstrained VBR (better for low-volume signals)
#define OPUS_SIGNAL_TYPE 3002 // OPUS_SIGNAL_MUSIC (better transient handling)
#define OPUS_BANDWIDTH 1105 // OPUS_BANDWIDTH_FULLBAND (20kHz, enabled by 128kbps bitrate)
#define OPUS_BANDWIDTH 1104 // OPUS_BANDWIDTH_SUPERWIDEBAND (16kHz, better quality at 128kbps)
#define OPUS_DTX 0 // DTX disabled (prevents audio drops)
#define OPUS_LSB_DEPTH 16 // 16-bit depth
@ -283,7 +283,7 @@ static int configure_alsa_device(snd_pcm_t *handle, const char *device_name) {
err = snd_pcm_hw_params_set_period_size_near(handle, params, &period_size, 0);
if (err < 0) return err;
snd_pcm_uframes_t buffer_size = period_size * 2; // Optimized: minimal buffer for low latency
snd_pcm_uframes_t buffer_size = period_size * 4; // 4 periods = 80ms buffer for stability
err = snd_pcm_hw_params_set_buffer_size_near(handle, params, &buffer_size);
if (err < 0) return err;
@ -373,7 +373,7 @@ int jetkvm_audio_capture_init() {
opus_encoder_ctl(encoder, OPUS_SET_DTX(OPUS_DTX));
opus_encoder_ctl(encoder, OPUS_SET_LSB_DEPTH(OPUS_LSB_DEPTH));
opus_encoder_ctl(encoder, OPUS_SET_INBAND_FEC(1));
opus_encoder_ctl(encoder, OPUS_SET_INBAND_FEC(0));
opus_encoder_ctl(encoder, OPUS_SET_PACKET_LOSS_PERC(20));
capture_initialized = 1;
@ -471,72 +471,6 @@ retry_read:
simd_clear_samples_s16(&pcm_buffer[pcm_rc * channels], remaining_samples);
}
// Find peak amplitude with NEON SIMD
uint32_t total_samples = frame_size * channels;
int16x8_t vmax = vdupq_n_s16(0);
uint32_t i;
for (i = 0; i + 8 <= total_samples; i += 8) {
int16x8_t v = vld1q_s16(&pcm_buffer[i]);
int16x8_t vabs = vabsq_s16(v);
vmax = vmaxq_s16(vmax, vabs);
}
// Horizontal max reduction (manual for ARMv7)
int16x4_t vmax_low = vget_low_s16(vmax);
int16x4_t vmax_high = vget_high_s16(vmax);
int16x4_t vmax_reduced = vmax_s16(vmax_low, vmax_high);
vmax_reduced = vpmax_s16(vmax_reduced, vmax_reduced);
vmax_reduced = vpmax_s16(vmax_reduced, vmax_reduced);
int16_t peak = vget_lane_s16(vmax_reduced, 0);
// Handle remaining samples
for (; i < total_samples; i++) {
int16_t abs_val = (pcm_buffer[i] < 0) ? -pcm_buffer[i] : pcm_buffer[i];
if (abs_val > peak) peak = abs_val;
}
// Apply gain if signal is weak (below -18dB = 4096) but above noise floor
// Noise gate: only apply gain if peak > 256 (below this is likely just noise)
// Target: boost to ~50% of range (16384) to improve SNR
if (peak > 256 && peak < 4096) {
float gain = 16384.0f / peak;
if (gain > 8.0f) gain = 8.0f; // Max 18dB boost
// Apply gain with NEON and saturation
float32x4_t vgain = vdupq_n_f32(gain);
for (i = 0; i + 8 <= total_samples; i += 8) {
int16x8_t v = vld1q_s16(&pcm_buffer[i]);
// Convert to float, apply gain, saturate back to int16
int32x4_t v_low = vmovl_s16(vget_low_s16(v));
int32x4_t v_high = vmovl_s16(vget_high_s16(v));
float32x4_t f_low = vcvtq_f32_s32(v_low);
float32x4_t f_high = vcvtq_f32_s32(v_high);
f_low = vmulq_f32(f_low, vgain);
f_high = vmulq_f32(f_high, vgain);
v_low = vcvtq_s32_f32(f_low);
v_high = vcvtq_s32_f32(f_high);
// Saturate to int16 range
int16x4_t result_low = vqmovn_s32(v_low);
int16x4_t result_high = vqmovn_s32(v_high);
vst1q_s16(&pcm_buffer[i], vcombine_s16(result_low, result_high));
}
// Handle remaining samples
for (; i < total_samples; i++) {
int32_t boosted = (int32_t)(pcm_buffer[i] * gain);
if (boosted > 32767) boosted = 32767;
if (boosted < -32768) boosted = -32768;
pcm_buffer[i] = (int16_t)boosted;
}
}
nb_bytes = opus_encode(encoder, pcm_buffer, frame_size, out, max_packet_size);
return nb_bytes;
}