Added HeaderParserAAC

Author: pschatzmann

examples/tests/codecs/test-mp3_parser/test-mp3_parser.ino

@@ -4,7 +4,7 @@
 #include "AudioTools/AudioLibs/AudioBoardStream.h" // for SD pins
 
 AudioSourceSD source("/", "", PIN_AUDIO_KIT_SD_CARD_CS);
-MP3HeaderParser mp3;
+HeaderParserMP3 mp3;
 
 void setup() {
   Serial.begin(115200);

src/AudioTools/AudioCodecs/HeaderParserAAC.h

@@ -0,0 +1,104 @@
+#pragma once
+#include "AudioTools/CoreAudio/AudioBasic/StrView.h"
+
+namespace audio_tools {
+
+/**
+ * @brief  AAC header parser to check if the data is a valid ADTS aac which
+ * can extract some relevant audio information.
+ * @ingroup codecs
+ * @ingroup decoder
+ * @author Phil Schatzmann
+ * @copyright GPLv3
+ */
+
+class HeaderParserAAC {
+  class AACHeader {
+   public:
+    uint8_t id;
+    uint8_t layer;
+    bool protection_absent;
+    uint8_t profile;
+    uint8_t sampling_freq_idx;
+    bool private_bit;
+    uint8_t channel_cfg;
+    bool original_copy;
+    // uint8_t home; // not used
+    uint8_t copyright_id_bit;
+    uint8_t copyright_id_start;
+    int frame_length;
+    uint8_t adts_buf_fullness;  // Used for bit reservoir, 0x7FF = VBR
+    int num_rawdata_blocks;     // Usually 00 (1 AAC frame per ADTS frame)
+  };
+
+ public:
+  /// parses the header string and returns true if this is a valid mp3 file
+  bool isValid(const uint8_t* data, int len) {
+    if (findSyncWord(data, len) == -1) {
+      LOGE("Could not find FrameSync");
+      return false;
+    }
+
+    header.id = (data[1] >> 3) & 0b1;
+    header.layer = (data[1] >> 1) & 0b11;
+    header.protection_absent = (data[1]) & 0b1;
+    header.profile = (data[2] >> 6) & 0b11;
+    header.sampling_freq_idx = (data[2] >> 2) & 0b1111;
+    header.private_bit = (data[2] >> 1) & 0b1;
+    header.channel_cfg = ((data[2] & 0b1) << 2) | (data[3] >> 6);
+    header.original_copy = (data[3] >> 5) & 0b1;
+    // header.home = (data[3] >> 4) & 0b1; // unused
+    //  parse adts_variable_header()
+    header.copyright_id_bit = (data[3] >> 3) & 0b1;
+    header.copyright_id_start = (data[3] >> 2) & 0b1;
+    header.frame_length =
+        ((data[3] & 0b11) << 11) | (data[4] << 3) | (data[5] >> 5);
+    header.adts_buf_fullness = ((data[5] & 0b11111) << 6) | (data[6] >> 2);
+    header.num_rawdata_blocks =
+        (data[6]) & 0b11;  // Usually 00 (1 AAC frame per ADTS frame)
+
+    bool is_valid = true;
+
+    is_valid = is_valid && header.sampling_freq_idx < 12;
+    is_valid = is_valid && header.channel_cfg < 8 && header.channel_cfg > 0;
+    is_valid = is_valid && header.profile < 3;  // 0: Main, 1: LC, 2: SSR
+    is_valid = is_valid && header.layer == 0;   // 0: ADTS
+    is_valid = is_valid && header.id <= 1;      // 0: MPEG-4, 1: MPEG-2
+
+    if (len >= header.frame_length + 11) {
+      is_valid = is_valid && findSyncWord(data + header.frame_length,
+                                          len - header.frame_length) != 0;
+    }
+    return is_valid;
+  }
+
+  uint16_t getSampleRate() const {
+    return sample_rates[header.sampling_freq_idx];
+  }
+
+  uint8_t getChannels() const { return header.channel_cfg; }
+
+  /// Determines the frame length
+  int getFrameLength() { return header.frame_length; }
+
+  /// Finds the mp3/aac sync word
+  int findSyncWord(const uint8_t* buf, size_t nBytes, uint8_t synch = 0xFF,
+                   uint8_t syncl = 0xF0) {
+    for (int i = 0; i < nBytes - 1; i++) {
+      if ((buf[i + 0] & synch) == synch && (buf[i + 1] & syncl) == syncl)
+        return i;
+    }
+    return -1;
+  }
+  int getRawDataBlocks() { return header.num_rawdata_blocks; }
+
+  AACHeader getHeader() { return header; }
+
+ protected:
+  const int sample_rates[13] = {96000, 88200, 64000, 48000, 44100, 32000, 24000,
+                                22050, 16000, 12000, 11025, 8000,  7350};
+
+  AACHeader header{0};
+};
+
+}  // namespace audio_tools

src/AudioTools/AudioCodecs/MP3HeaderParser.h renamed to src/AudioTools/AudioCodecs/HeaderParserMP3.h

@@ -14,7 +14,7 @@ namespace audio_tools {
  * @copyright GPLv3
  */
 
-class MP3HeaderParser {
+class HeaderParserMP3 {
   // MPEG audio frame header
   // variables are declared in their serialized order
   // includes crc value

src/AudioTools/CoreAudio/AudioMetaData/MimeDetector.h

@@ -1,6 +1,7 @@
 #pragma once
 
-#include "AudioTools/AudioCodecs/MP3HeaderParser.h"
+#include "AudioTools/AudioCodecs/HeaderParserMP3.h"
+#include "AudioTools/AudioCodecs/HeaderParserAAC.h"
 #include "AudioTools/CoreAudio/AudioBasic/StrView.h"
 
 namespace audio_tools {
@@ -74,7 +75,7 @@ class MimeDetector {
     if (!(start[0] == 0xFF &&
           (start[1] == 0xF0 || start[1] == 0xF1 || start[1] == 0xF9)))
       return false;
-    MP3HeaderParser mp3;
+    HeaderParserMP3 mp3;
     // it should start with a synch word
     if (mp3.findSyncWord((const uint8_t*)start, len) != 0) {
       return false;
@@ -92,7 +93,7 @@ class MimeDetector {
   }
 
   static bool checkMP3Ext(uint8_t* start, size_t len) {
-    MP3HeaderParser mp3;
+    HeaderParserMP3 mp3;
     return mp3.isValid(start, len);
   }