Cleanup FFmpeg arguments and bitrate logic (was specified too late af…

…ter the destination)

README.md

@@ -143,23 +143,27 @@ 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`.
+You can specify the following options:
 
-#### format
+##### 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 }
+opts = { format: 'webm' }
 ```
 
-#### bitrate
+#### Variable bitrate
 
-The default export bitrate depends on the codec used. You can specify an export bitrate by adding a `bitrate` option. Check [ffmpeg docmentation](https://trac.ffmpeg.org/wiki/Encode/H.264) for more information.
+You can specify a variable bitrate (a.k.a. average bitrate, or target bitrate) by using the `bitrate` option.
+Check the [ffmpeg docmentation](https://trac.ffmpeg.org/wiki/Encode/H.264) for more information.
 
 ```js
-opts = { bitrate: xxx }
+opts = { bitrate: '1200k' }
 ```
 
+##### Conversion progress
+
 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

@@ -8,6 +8,9 @@ const gmargs = require('./gmargs')
 const ffmpeg = require('./ffmpeg')
 
 const GIF_FILE = /\.gif$/i
+const DEFAULT_PHOTO_QUALITY = 90 // percent
+const DEFAULT_AUDIO_BITRATE = '96k'
+const DEFAULT_VIDEO_FPS = 25
 
 /*
   Convert and/or resize an image
@@ -62,7 +65,7 @@ exports.image = function (source, target, options, callback) {
   }
 
   // default quality, for typical web-friendly sizes
-  image.quality(options.quality || 90)
+  image.quality(options.quality || DEFAULT_PHOTO_QUALITY)
   // apply custom post-processing arguments (sharpen, brightness...)
   gmargs.apply(image, options.args)
   // write the output image
@@ -76,26 +79,33 @@ exports.image = function (source, target, options, callback) {
 exports.video = function (source, target, options, callback) {
   // create target folder if needed
   mkdirp.sync(path.dirname(target))
-  const args = ['-i', source, '-r', '25', '-vsync', '2', '-movflags', '+faststart', '-y', target, '-ab', '96k']
+
+  // common options
+  const args = ['-i', source, '-r', DEFAULT_VIDEO_FPS, '-vsync', '2', '-movflags', '+faststart', '-ab', DEFAULT_AUDIO_BITRATE]
+
   // output to mp4 or webm which are well read on the web
   if (options.format === 'webm') {
-    args.push('-f', 'webm', '-vcodec', 'libvpx-vp9')
     args.push('-f', 'webm', '-vcodec', 'libvpx-vp9', '-strict', '-2')
   } else {
     args.push('-f', 'mp4', '-vcodec', 'libx264')
   }
 
-  // set video bitrate
+  // set average bitrate or perceptual quality
   if (options.bitrate) {
     args.push('-b:v', options.bitrate)
+  } else {
+    // TODO: add configurable CRF value
+    args.push('-b:v', 0, '-crf', 20)
   }
 
   // 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')
-  } else {
-    args.push('-vb', '1200k')
+    args.push('-vf', 'yadif=1')
   }
+
+  // target filename
+  args.push('-y', target)
+
   // return a EventEmitter to follow progress, since this can take a long time
   return ffmpeg.exec(args, callback)
 }

test/diff.js

@@ -32,7 +32,7 @@ exports.video = function (test, args) {
   const expected = `test-data/expected/${args.expect}`
   convert.video(input, actual, args.options, (err) => {
     if (err) return test.end(err)
-    convert.still(actual, `${actual}.jpg`, args.options, (err) => {
+    convert.still(actual, `${actual}.jpg`, {}, (err) => {
       if (err) return test.end(err)
       compareImage(test, `${expected}.jpg`, `${actual}.jpg`)
     })

test/video.js

@@ -21,6 +21,28 @@ tape('can convert a video to webm', (test) => {
   })
 })
 
+tape('can convert to MP4 with a target bitrate', (test) => {
+  diff.video(test, {
+    input: 'videos/countdown.mp4',
+    expect: 'videos/countdown-bitrate.mp4',
+    options: {
+      format: 'mp4',
+      bitrate: '100k'
+    }
+  })
+})
+
+tape('can convert to WEBM with a target bitrate', (test) => {
+  diff.video(test, {
+    input: 'videos/countdown.mp4',
+    expect: 'videos/countdown-bitrate.webm',
+    options: {
+      format: 'webm',
+      bitrate: '100k'
+    }
+  })
+})
+
 tape('can report progress when processing videos', (t) => {
   const report = []
   const input = 'test-data/input/videos/big_buck_bunny.mp4'