#1332: Improve the poster selection for audio/music based torrent,

aiming to get the cover-art selected as the torrent poster.

src/renderer/lib/torrent-poster.js

@@ -3,6 +3,13 @@ module.exports = torrentPoster
 const captureFrame = require('capture-frame')
 const path = require('path')
 
+const mediaExtensions = {
+  audio: ['.aac', '.asf', '.flac', '.m2a', '.m4a', '.mp2', '.mp4', '.mp3', '.oga', '.ogg', '.opus',
+    '.wma', '.wav', '.wv', '.wvp'],
+  video: ['.mp4', '.m4v', '.webm', '.mov', '.mkv'],
+  image: ['.gif', '.jpg', '.jpeg', '.png']
+}
+
 function torrentPoster (torrent, cb) {
   // First, try to use a poster image if available
   const posterFile = torrent.files.filter(function (file) {
@@ -10,32 +17,95 @@ function torrentPoster (torrent, cb) {
   })[0]
   if (posterFile) return torrentPosterFromImage(posterFile, torrent, cb)
 
-  // Second, try to use the largest video file
-  // Filter out file formats that the <video> tag definitely can't play
-  const videoFile = getLargestFileByExtension(torrent, ['.mp4', '.m4v', '.webm', '.mov', '.mkv'])
-  if (videoFile) return torrentPosterFromVideo(videoFile, torrent, cb)
+  // 'score' each media type based on total size present in torrent
+  const bestScore = ['audio', 'video', 'image'].map(mediaType => {
+    return {
+      type: mediaType,
+      size: calculateDataLengthByExtension(torrent, mediaExtensions[mediaType])}
+  }).sort((a, b) => { // sort descending on size
+    return b.size - a.size
+  })[0]
 
-  // Third, try to use the largest image file
-  const imgFile = getLargestFileByExtension(torrent, ['.gif', '.jpg', '.jpeg', '.png'])
-  if (imgFile) return torrentPosterFromImage(imgFile, torrent, cb)
+  if (bestScore.size === 0) {
+    // Admit defeat, no video, audio or image had a significant presence
+    return cb(new Error('Cannot generate a poster from any files in the torrent'))
+  }
 
-  // TODO: generate a waveform from the largest sound file
-  // Finally, admit defeat
-  return cb(new Error('Cannot generate a poster from any files in the torrent'))
+  // Based on which media type is dominant we select the corresponding poster function
+  switch (bestScore.type) {
+    case 'audio':
+      return torrentPosterFromAudio(torrent, cb)
+    case 'image':
+      return torrentPosterFromImage(torrent, cb)
+    case 'video':
+      return torrentPosterFromVideo(torrent, cb)
+  }
+}
+
+/**
+ * Calculate the total data size of file matching one of the provided extensions
+ * @param torrent
+ * @param extensions List of extension to match
+ * @returns {number} total size, of matches found (>= 0)
+ */
+function calculateDataLengthByExtension (torrent, extensions) {
+  const files = filterOnExtension(torrent, extensions)
+  if (files.length === 0) return 0
+  return files
+    .map(file => file.length)
+    .reduce((a, b) => {
+      return a + b
+    })
 }
 
 function getLargestFileByExtension (torrent, extensions) {
-  const files = torrent.files.filter(function (file) {
-    const extname = path.extname(file.name).toLowerCase()
-    return extensions.indexOf(extname) !== -1
-  })
+  const files = filterOnExtension(torrent, extensions)
   if (files.length === 0) return undefined
-  return files.reduce(function (a, b) {
+  return files.reduce((a, b) => {
     return a.length > b.length ? a : b
   })
 }
 
-function torrentPosterFromVideo (file, torrent, cb) {
+function filterOnExtension (torrent, extensions) {
+  return torrent.files.filter(file => {
+    const extname = path.extname(file.name).toLowerCase()
+    return extensions.indexOf(extname) !== -1
+  })
+}
+
+function scoreCoverFile (file) {
+  const name = path.basename(file.name, path.extname(file.name)).toLowerCase()
+  switch (name) {
+    case 'cover': return 100
+    case 'folder': return 95
+    case 'front': return 85
+    case 'front-cover': return 90
+    case 'back': return 40
+    default: return 0
+  }
+}
+
+function torrentPosterFromAudio (torrent, cb) {
+  const imageFiles = filterOnExtension(torrent, mediaExtensions.image)
+
+  const bestCover = imageFiles.map(file => {
+    return {
+      file: file,
+      score: scoreCoverFile(file)
+    }
+  }).sort((a, b) => {
+    return b.score - a.score
+  })
+
+  if (bestCover.length < 1) return cb(new Error('Generated poster contains no data'))
+
+  const extname = path.extname(bestCover[0].file.name)
+  bestCover[0].file.getBuffer((err, buf) => cb(err, buf, extname))
+}
+
+function torrentPosterFromVideo (torrent, cb) {
+  const file = getLargestFileByExtension(torrent, mediaExtensions.video)
+
   const index = torrent.files.indexOf(file)
 
   const server = torrent.createServer(0)
@@ -77,7 +147,9 @@ function torrentPosterFromVideo (file, torrent, cb) {
   }
 }
 
-function torrentPosterFromImage (file, torrent, cb) {
+function torrentPosterFromImage (torrent, cb) {
+  const file = getLargestFileByExtension(torrent, mediaExtensions.image)
+
   const extname = path.extname(file.name)
   file.getBuffer((err, buf) => cb(err, buf, extname))
 }