feat: add webm support

README.md

@@ -139,7 +139,14 @@ This method supports all  the same options as `.image()`.
 ```
 
 Transcodes the video in `source` to a web-friendly format and lower bitrate, and writes it in `target`.
-Currently doesn't support any options, simply pass an empty hash (`{}`).
+
+#### format
+
+The default export format is mp4. You can specify an export format by adding a `format` option whose value can be `mp4` or `webm`.
+
+```js
+opts = { format: webm }
+```
 
 The `.video()` call returns an [EventEmitter](https://nodejs.org/api/events.html)
 to follow the progress of the conversion, since it can take a long time.

lib/index.js

@@ -76,8 +76,13 @@ exports.image = function (source, target, options, callback) {
 exports.video = function (source, target, options, callback) {
   // create target folder if needed
   mkdirp.sync(path.dirname(target))
-  // always output to mp4 which is well read on the web
-  const args = ['-i', source, '-r', '25', '-vsync', '2', '-movflags', '+faststart', '-y', target, '-f', 'mp4', '-vcodec', 'libx264', '-ab', '96k']
+  const args = ['-i', source, '-r', '25', '-vsync', '2', '-movflags', '+faststart', '-y', target, '-ab', '96k']
+  // output to mp4 or webm which are well read on the web
+  if (options.format === 'webm') {
+    args.push('-f', 'webm', '-vcodec', 'libvpx-vp9')
+  } else {
+    args.push('-f', 'mp4', '-vcodec', 'libx264')
+  }
   // AVCHD/MTS videos need a full-frame export to avoid interlacing artefacts
   if (path.extname(source).toLowerCase() === '.mts') {
     args.push('-vf', 'yadif=1', '-qscale:v', '4')

test/video.js

@@ -11,6 +11,16 @@ tape('can downsample a video for a smaller filesize', (test) => {
   })
 })
 
+tape('can convert a video to webm', (test) => {
+  diff.video(test, {
+    input: 'videos/short.mp4',
+    expect: 'videos/short.webm',
+    options: {
+      format: 'webm'
+    }
+  })
+})
+
 tape('can report progress when processing videos', (t) => {
   const report = []
   const input = 'test-data/input/videos/big_buck_bunny.mp4'