Add metadata to compile output, fixes #30

README.md

@@ -166,11 +166,41 @@ If no metadata is available, `meta` will be set to `null` in the result if the o
 
 ### Compiling
 
-Compiles JSON from the above format back into a WebVTT string.
+Compiles JSON from the above format back into a WebVTT string. If a `meta` key is in the input,
+it will be compiled as well. The `meta` value must be an object and each key and value must be a string.
 
 If the object is missing any attributes, the compiler will throw a `CompilerError` exception. So
 for safety, calls to `compile` should be in `try catch`.
 
+```javascript
+const input = {
+  meta: {
+    Kind: 'captions',
+    Language: 'en'
+  },
+  cues: [{
+    end: 140,
+    identifier: '1',
+    start: 135.001,
+    text: 'Hello world',
+    styles: ''
+  }],
+  valid: true
+};
+
+const result = compile(input);
+
+/*
+WEBVTT
+Kind: captions
+Language: en
+
+1
+00:02:15.001 --> 00:02:20.000
+Hello world
+*/
+```
+
 ### Segmenting
 
 Segments a subtitle according to how it should be segmented for HLS subtitles.

lib/compiler.js

@@ -31,6 +31,20 @@ function compile (input) {
 
   let output = 'WEBVTT\n';
 
+  if (input.meta) {
+    if (typeof input.meta !== 'object' || Array.isArray(input.meta)) {
+      throw new CompilerError('Metadata must be an object');
+    }
+
+    Object.entries(input.meta).forEach((i) => {
+      if (typeof i[1] !== 'string') {
+        throw new CompilerError(`Metadata value for "${i[0]}" must be string`);
+      }
+
+      output += `${i[0]}: ${i[1]}\n`;
+    });
+  }
+
   input.cues.forEach((cue) => {
     output += '\n';
     output += compileCue(cue);

test/compiler.test.js

@@ -405,4 +405,46 @@ Hello world
 
     compile(input).should.equal(output);
   });
+
+  it('should compile metadata', () => {
+    const input = {
+      meta: {
+        Kind: 'captions',
+        Language: 'en'
+      },
+      cues: [{
+        end: 140,
+        identifier: '1',
+        start: 135.001,
+        text: 'Hello world',
+        styles: ''
+      }],
+      valid: true
+    };
+
+    const output = `WEBVTT
+Kind: captions
+Language: en
+
+1
+00:02:15.001 --> 00:02:20.000
+Hello world
+`;
+
+    compile(input).should.equal(output);
+  });
+
+  it('should not compile non-object metadata', () => {
+    (() => {
+      compile({ meta: [], cues: [], valid: true });
+    })
+      .should.throw(compilerError, /Metadata must be an object/);
+  });
+
+  it('should not compile non-string metadata values', () => {
+    (() => {
+      compile({ meta: { foo: [] }, cues: [], valid: true });
+    })
+      .should.throw(compilerError, /Metadata value for "foo" must be string/);
+  });
 });