#782 Support Adaptive Multi-Rate (AMR) audio codec

README.md

@@ -48,6 +48,7 @@ If you find this project useful and would like to support its development, consi
 | ------------- |---------------------------------| -------------------------------------------------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------:|
 | AIFF / AIFF-C | Audio Interchange File Format   | [:link:](https://wikipedia.org/wiki/Audio_Interchange_File_Format) | <img src="https://upload.wikimedia.org/wikipedia/commons/8/84/Apple_Computer_Logo_rainbow.svg" width="40" alt="Apple rainbow logo">           |
 | AAC           | ADTS / Advanced Audio Coding    | [:link:](https://en.wikipedia.org/wiki/Advanced_Audio_Coding)      | <img src="https://svgshare.com/i/UT8.svg" width="40" alt="AAC logo">                                                                          |
+| AMR           | Adaptive Multi-Rate audio codec | [:link:](https://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_codec) | <img src="https://foreverhits.files.wordpress.com/2015/05/ape_audio.jpg" width="40" alt="Monkey's Audio logo">                           |
 | APE           | Monkey's Audio                  | [:link:](https://wikipedia.org/wiki/Monkey's_Audio)                | <img src="https://foreverhits.files.wordpress.com/2015/05/ape_audio.jpg" width="40" alt="Monkey's Audio logo">                                |
 | ASF           | Advanced Systems Format         | [:link:](https://wikipedia.org/wiki/Advanced_Systems_Format)       |                                                                                                                                               |
 | BWF           | Broadcast Wave Format           | [:link:](https://en.wikipedia.org/wiki/Broadcast_Wave_Format)      |                                                                                                                                               |

lib/ParserFactory.ts

@@ -220,6 +220,9 @@ function getParserIdForMimeType(httpContentType: string | undefined): ParserType
 
         case 'dsf':
           return 'dsf';
+
+        case 'amr':
+          return 'amr';
       }
       break;
 

lib/amr/AmrParser.ts

@@ -0,0 +1,58 @@
+import { BasicParser } from '../common/BasicParser';
+import { AnsiStringType } from 'token-types';
+import * as initDebug from 'debug';
+import { FrameHeader } from './AmrToken';
+
+const debug = initDebug('music-metadata:parser:AMR');
+
+/**
+ * There are 8 varying levels of compression. First byte of the frame specifies CMR
+ * (codec mode request), values 0-7 are valid for AMR. Each mode have different frame size.
+ * This table reflects that fact.
+ */
+const m_block_size = [12, 13, 15, 17, 19, 20, 26, 31, 5, 0, 0, 0, 0, 0, 0, 0];
+
+/**
+ * Adaptive Multi-Rate audio codec
+ */
+export class AmrParser extends BasicParser {
+
+  public async parse(): Promise<void> {
+    const magicNr = await this.tokenizer.readToken(new AnsiStringType(5));
+    if (magicNr !== '#!AMR') {
+      throw new Error('Invalid AMR file: invalid MAGIC number');
+    }
+    this.metadata.setFormat('container', 'AMR');
+    this.metadata.setFormat('codec', 'AMR');
+    this.metadata.setFormat('sampleRate', 8000);
+    this.metadata.setFormat('bitrate', 64000);
+    this.metadata.setFormat('numberOfChannels', 1);
+
+    let total_size = 0;
+    let frames = 0;
+
+    const assumedFileLength = this.tokenizer.fileInfo ? this.tokenizer.fileInfo.size : Number.MAX_SAFE_INTEGER;
+
+    if (this.options.duration) {
+      while (this.tokenizer.position < assumedFileLength) {
+        const header = await this.tokenizer.readToken(FrameHeader);
+        if (header.frameType === 15 || (header.frameType > 8 && header.frameType < 15)) {
+          debug(`Found no-data frame, ft: ${header.frameType}. Skipping`);
+        }
+        else {
+          debug(`Found data frame, ft: ${header.frameType}, frames: ${frames}, size: ${m_block_size[header.frameType]}`);
+          /* increase number of frames */
+          ++frames;
+        }
+        /* first byte is rate mode. each rate mode has frame of given length. look it up. */
+        const size = m_block_size[header.frameType];
+
+        /* FIXME: there is something inherently broken with how I calculate frames here. Need to revise it. */
+        total_size += size + 1;
+        if (total_size > assumedFileLength) break;
+        await this.tokenizer.ignore(size);
+      }
+      this.metadata.setFormat('duration', frames * 0.02);
+    }
+  }
+}

lib/amr/AmrToken.ts

@@ -0,0 +1,24 @@
+import { IGetToken } from 'strtok3/lib/core';
+import common from '../common/Util';
+
+interface IFrameHeader {
+  frameType: number;
+  fqi: boolean;
+}
+
+/**
+ * ID3v2 header
+ * Ref: http://id3.org/id3v2.3.0#ID3v2_header
+ * ToDo
+ */
+export const FrameHeader: IGetToken<IFrameHeader > = {
+  len: 1,
+
+  get: (buf, off): IFrameHeader => {
+    return {
+      // ID3v2/file identifier   "ID3"
+      frameType: common.getBitAllignedNumber(buf, off, 4, 4),
+      fqi: common.strtokBITSET.get(buf, off, 3)
+    };
+  }
+};

lib/type.ts

@@ -596,7 +596,8 @@ export type ParserType =
   | 'dsf'
   | 'dsdiff'
   | 'adts'
-  | 'matroska';
+  | 'matroska'
+  | 'amr';
 
 export interface IOptions {
 

test/test-file-amr.ts

@@ -0,0 +1,17 @@
+import { assert } from 'chai';
+import * as mm from '../lib';
+import * as path from 'path';
+
+describe('Parse Adaptive Multi-Rate (AMR) audio codec', () => {
+
+  const amrSamplePath = path.join(__dirname, 'samples', 'amr');
+
+  it('Decode AMR file', async () => {
+    const  {format} = await mm.parseFile(path.join(amrSamplePath, 'sample.amr'), {duration: true});
+    assert.strictEqual(format.sampleRate, 8000, 'format.sampleRate');
+    assert.strictEqual(format.numberOfChannels, 1, 'format.numberOfChannels');
+    assert.strictEqual(format.bitrate, 64000, 'format.bitrate');
+    assert.approximately(format.duration, 35.340, 0.0005, 'format.duration');
+  });
+
+});