mirror of https://github.com/jetkvm/kvm.git
Fix: eliminate audio warping by auto-adapting to actual device sample rate
Root cause: ALSA was silently using a different sample rate than configured, causing severe pitch/speed distortion (the "cassette player" warping effect). The bug occurred when: - User configured 48 kHz in UI - HDMI source output 44.1 kHz audio - set_rate() failed, set_rate_near() chose 44.1 kHz - Code never checked what rate was actually set - Opus encoder created for 48 kHz but received 44.1 kHz audio - Result: ~9% pitch shift and timing mismatch Fix: - Always use set_rate_near() and check the actual rate returned - Pass detected rate and frame size to Opus encoder/decoder creation - Avoid modifying global state to prevent capture/playback interference - Recalculate frame_size for 20ms at the actual rate - Verify rate after hw_params application - Add detailed logging for rate adaptation This ensures Opus encoder/decoder use the correct rate matching the hardware, regardless of what the HDMI source outputs.
This commit is contained in:
Alex P
parent
11dadebb93
commit
236291a454
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@ -254,12 +254,15 @@ static int safe_alsa_open(snd_pcm_t **handle, const char *device, snd_pcm_stream
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}
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/**
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* Configure ALSA device (S16_LE @ 48kHz stereo with optimized buffering)
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* Configure ALSA device (S16_LE @ variable rate stereo with optimized buffering)
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* @param handle ALSA PCM handle
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* @param device_name Unused (for debugging only)
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* @param device_name Device name for logging
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* @param actual_rate_out Pointer to store the actual rate the device was configured to use
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* @param actual_frame_size_out Pointer to store the actual frame size (samples per channel)
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* @return 0 on success, negative error code on failure
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*/
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static int configure_alsa_device(snd_pcm_t *handle, const char *device_name) {
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static int configure_alsa_device(snd_pcm_t *handle, const char *device_name,
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unsigned int *actual_rate_out, uint16_t *actual_frame_size_out) {
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snd_pcm_hw_params_t *params;
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snd_pcm_sw_params_t *sw_params;
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int err;
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@ -281,14 +284,30 @@ static int configure_alsa_device(snd_pcm_t *handle, const char *device_name) {
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err = snd_pcm_hw_params_set_channels(handle, params, channels);
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if (err < 0) return err;
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err = snd_pcm_hw_params_set_rate(handle, params, sample_rate, 0);
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if (err < 0) {
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unsigned int rate = sample_rate;
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err = snd_pcm_hw_params_set_rate_near(handle, params, &rate, 0);
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if (err < 0) return err;
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unsigned int requested_rate = sample_rate;
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unsigned int actual_rate = sample_rate;
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err = snd_pcm_hw_params_set_rate_near(handle, params, &actual_rate, 0);
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if (err < 0) return err;
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uint16_t actual_frame_size = frame_size;
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if (actual_rate != requested_rate) {
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fprintf(stderr, "INFO: %s: Requested sample rate %u Hz, device supports %u Hz (%.1f%% difference)\n",
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device_name, requested_rate, actual_rate, ((float)actual_rate - requested_rate) / requested_rate * 100.0f);
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fprintf(stderr, "INFO: %s: Adapting to device rate %u Hz to avoid pitch/speed distortion\n", device_name, actual_rate);
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fflush(stderr);
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actual_frame_size = (actual_rate * 20) / 1000;
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if (channels == 2) {
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if (actual_frame_size < 480) actual_frame_size = 480;
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if (actual_frame_size > 2880) actual_frame_size = 2880;
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}
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fprintf(stderr, "INFO: %s: Adjusted frame size to %u samples (20ms at %u Hz)\n",
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device_name, actual_frame_size, actual_rate);
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fflush(stderr);
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}
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snd_pcm_uframes_t period_size = frame_size;
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snd_pcm_uframes_t period_size = actual_frame_size;
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if (period_size < 64) period_size = 64;
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err = snd_pcm_hw_params_set_period_size_near(handle, params, &period_size, 0);
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@ -301,6 +320,14 @@ static int configure_alsa_device(snd_pcm_t *handle, const char *device_name) {
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err = snd_pcm_hw_params(handle, params);
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if (err < 0) return err;
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unsigned int verified_rate = 0;
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err = snd_pcm_hw_params_get_rate(params, &verified_rate, 0);
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if (err < 0 || verified_rate != actual_rate) {
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fprintf(stderr, "WARNING: %s: Rate verification failed - expected %u Hz, got %u Hz\n",
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device_name, actual_rate, verified_rate);
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fflush(stderr);
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}
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err = snd_pcm_sw_params_current(handle, sw_params);
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if (err < 0) return err;
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@ -313,7 +340,13 @@ static int configure_alsa_device(snd_pcm_t *handle, const char *device_name) {
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err = snd_pcm_sw_params(handle, sw_params);
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if (err < 0) return err;
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return snd_pcm_prepare(handle);
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err = snd_pcm_prepare(handle);
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if (err < 0) return err;
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if (actual_rate_out) *actual_rate_out = actual_rate;
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if (actual_frame_size_out) *actual_frame_size_out = actual_frame_size;
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return 0;
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}
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// AUDIO OUTPUT PATH FUNCTIONS (TC358743 HDMI Audio → Client Speakers)
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@ -355,7 +388,9 @@ int jetkvm_audio_capture_init() {
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return -1;
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}
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err = configure_alsa_device(pcm_capture_handle, "capture");
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unsigned int actual_rate = 0;
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uint16_t actual_frame_size = 0;
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err = configure_alsa_device(pcm_capture_handle, "capture", &actual_rate, &actual_frame_size);
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if (err < 0) {
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snd_pcm_close(pcm_capture_handle);
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pcm_capture_handle = NULL;
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@ -363,8 +398,12 @@ int jetkvm_audio_capture_init() {
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return -2;
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}
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fprintf(stderr, "INFO: capture: Initializing Opus encoder at %u Hz, %u channels, frame size %u\n",
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actual_rate, channels, actual_frame_size);
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fflush(stderr);
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int opus_err = 0;
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encoder = opus_encoder_create(sample_rate, channels, OPUS_APPLICATION_AUDIO, &opus_err);
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encoder = opus_encoder_create(actual_rate, channels, OPUS_APPLICATION_AUDIO, &opus_err);
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if (!encoder || opus_err != OPUS_OK) {
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if (pcm_capture_handle) {
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snd_pcm_close(pcm_capture_handle);
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@ -534,7 +573,9 @@ int jetkvm_audio_playback_init() {
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}
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}
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err = configure_alsa_device(pcm_playback_handle, "playback");
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unsigned int actual_rate = 0;
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uint16_t actual_frame_size = 0;
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err = configure_alsa_device(pcm_playback_handle, "playback", &actual_rate, &actual_frame_size);
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if (err < 0) {
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snd_pcm_close(pcm_playback_handle);
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pcm_playback_handle = NULL;
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@ -542,8 +583,12 @@ int jetkvm_audio_playback_init() {
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return -1;
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}
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fprintf(stderr, "INFO: playback: Initializing Opus decoder at %u Hz, %u channels, frame size %u\n",
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actual_rate, channels, actual_frame_size);
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fflush(stderr);
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int opus_err = 0;
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decoder = opus_decoder_create(sample_rate, channels, &opus_err);
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decoder = opus_decoder_create(actual_rate, channels, &opus_err);
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if (!decoder || opus_err != OPUS_OK) {
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snd_pcm_close(pcm_playback_handle);
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pcm_playback_handle = NULL;
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