fix: use yuv420p subsampling for best compatibility

Fixes #26

lib/video/ffargs.js

@@ -64,13 +64,8 @@ exports.prepare = function (source, target, options) {
     args.push('-b:v', 0, '-crf', exports.crf(quality, encoder))
   }
 
-  // AVCHD/MTS videos need a full-frame export to avoid interlacing artefacts
-  if (path.extname(source).toLowerCase() === '.mts') {
-    args.push('-vf', 'yadif=1')
-  } else if ((options.bitrate) && (options.hwaccel === 'vaapi')) {
-    // if VAAPI + here you to add the scaling option too ",scale_vaapi=1280:-1"
-    args.push('-vf', 'format=nv12|vaapi,hwupload')
-  }
+  const filters = exports.videoFilters(source, options)
+  args.push('-vf', filters)
 
   // target filename
   args.push(target)
@@ -85,3 +80,22 @@ exports.crf = function (percent, encoder) {
   const inverted = ENCODER_CRF[encoder].max - proportion
   return Math.floor(inverted)
 }
+
+// Configure video filters
+exports.videoFilters = function (source, options) {
+  const filters = []
+  // AVCHD/MTS videos need a full-frame export to avoid interlacing artefacts
+  if (path.extname(source).toLowerCase() === '.mts') {
+    filters.push('yadif=1')
+  }
+  // Configure subsampling and hardware acceleration
+  if ((options.bitrate) && (options.hwaccel === 'vaapi')) {
+    // VAAPI requires nv12, which is equivalent to yuv420p for an h264 stream
+    // Here we could add scaling option too e.g. ",scale_vaapi=1280:-1"
+    filters.push('format=nv12|vaapi', 'hwupload')
+  } else {
+    // Standard case: use YUV420p which has the best compatibility
+    filters.push('format=yuv420p')
+  }
+  return filters.join(',')
+}

test/unit/ffargs.test.js

@@ -24,10 +24,32 @@ describe('ffargs', () => {
     should(ffargs.crf(100, 'vpx')).eql(15)
   })
 
-  it('handles MTS interlacing', () => {
-    const args = ffargs.prepare('source.mts', 'target.mp4', {})
-    const str = args.join(' ')
-    should(str).match(/-vf yadif=1/)
+  describe('video filters', () => {
+    it('uses yuv420p chroma subsampling by default', () => {
+      // videos from recent iPhones use yuv420p10le
+      // once converted to h264 they don't play well in browsers / macOS finder
+      // ffmpeg recommends using yuv420p for best compatibility
+      // see http://trac.ffmpeg.org/wiki/Encode/H.264
+      // and https://trac.ffmpeg.org/wiki/Encode/VP9
+      const vf = ffargs.videoFilters('source.mov', {})
+      should(vf).match(/format=yuv420p/)
+    })
+
+    it('handles MTS interlacing', () => {
+      const vf = ffargs.videoFilters('source.mts', {})
+      should(vf).match(/yadif=1,format=yuv420p/)
+    })
+
+    it('handles VAAPI hardware acceleration', () => {
+      const vf = ffargs.videoFilters('source.mov', { hwaccel: 'vaapi', bitrate: '1200k' })
+      should(vf).match(/format=nv12\|vaapi,hwupload/)
+    })
+
+    it('passes the video filter argument', () => {
+      const args = ffargs.prepare('source.mov', 'target.mp4', {})
+      const str = args.join(' ')
+      should(str).match(/-vf format=yuv420p/)
+    })
   })
 
   describe('framerate', () => {