MP3File: Add rms_level property

This lets a music player show it vu-meter style

2 files changed, 13 insertions, 0 deletions

diff --git a/shared-module/audiomp3/MP3File.c b/shared-module/audiomp3/MP3File.c
index 390ba2544..515aa0086 100644
--- a/shared-module/audiomp3/MP3File.c
+++ b/shared-module/audiomp3/MP3File.c
@@ -29,6 +29,7 @@
 
 #include <stdint.h>
 #include <string.h>
+#include <math.h>
 
 #include "py/mperrno.h"
 #include "py/runtime.h"
@@ -339,3 +340,13 @@ void audiomp3_mp3file_get_buffer_structure(audiomp3_mp3file_obj_t* self, bool si
         *spacing = 1;
     }
 }
+
+float common_hal_audiomp3_mp3file_get_rms_level(audiomp3_mp3file_obj_t* self) {
+    float sumsq = 0.f;
+    // Assumes no DC component to the audio.  Is that a safe assumption?
+    int16_t *buffer = (int16_t *)(void *)self->buffers[self->buffer_index];
+    for(size_t i=0; i<self->frame_buffer_size / sizeof(int16_t); i++) {
+        sumsq += (float)buffer[i] * buffer[i];
+    }
+    return sqrtf(sumsq) / (self->frame_buffer_size / sizeof(int16_t));
+}
diff --git a/shared-module/audiomp3/MP3File.h b/shared-module/audiomp3/MP3File.h
index 9d99e8d1f..9ee1d0949 100644
--- a/shared-module/audiomp3/MP3File.h
+++ b/shared-module/audiomp3/MP3File.h
@@ -67,4 +67,6 @@ void audiomp3_mp3file_get_buffer_structure(audiomp3_mp3file_obj_t* self, bool si
                                            bool* single_buffer, bool* samples_signed,
                                            uint32_t* max_buffer_length, uint8_t* spacing);
 
+float audiomp3_mp3file_get_rms_level(audiomp3_mp3file_obj_t* self);
+
 #endif // MICROPY_INCLUDED_SHARED_MODULE_AUDIOIO_MP3FILE_H