Adding download tab and download manager, ffmpeg in worker thread

server/utils/ffmpegHelpers.js

@@ -0,0 +1,37 @@
+const fs = require('fs-extra')
+
+function escapeSingleQuotes(path) {
+  // return path.replace(/'/g, '\'\\\'\'')
+  return path.replace(/\\/g, '/').replace(/ /g, '\\ ').replace(/'/g, '\\\'')
+}
+
+// Returns first track start time
+// startTime is for streams starting an encode part-way through an audiobook
+async function writeConcatFile(tracks, outputPath, startTime = 0) {
+  var trackToStartWithIndex = 0
+  var firstTrackStartTime = 0
+
+  // Find first track greater than startTime
+  if (startTime > 0) {
+    var currTrackEnd = 0
+    var startingTrack = tracks.find(t => {
+      currTrackEnd += t.duration
+      return startTime < currTrackEnd
+    })
+    if (startingTrack) {
+      firstTrackStartTime = currTrackEnd - startingTrack.duration
+      trackToStartWithIndex = startingTrack.index
+    }
+  }
+
+  var tracksToInclude = tracks.filter(t => t.index >= trackToStartWithIndex)
+  var trackPaths = tracksToInclude.map(t => {
+    var line = 'file ' + escapeSingleQuotes(t.fullPath) + '\n' + `duration ${t.duration}`
+    return line
+  })
+  var inputstr = trackPaths.join('\n\n')
+  await fs.writeFile(outputPath, inputstr)
+
+  return firstTrackStartTime
+}
+module.exports.writeConcatFile = writeConcatFile