#16 Preview video generation

.gitignore

@@ -3,4 +3,5 @@ bin/
 media/
 dist/
 pouch__all_dbs__/
+_previews/
 _media

README.md

@@ -38,6 +38,10 @@ db.changes({
 });
 ```
 
+### Preview Videos
+This tool is able to generate low resolution webm preview videos of all media, intended to be used in web based clients.
+They are generated in the background after the media is found or detected to have changed, so may not be available immediately.
+They can be accessed via the following url format `/media/preview/<name>`
 
 Development
 -----------

src/app.js

@@ -2,6 +2,7 @@ const express = require('express')
 const pinoHttp = require('pino-http')
 const PouchDB = require('pouchdb-node')
 const util = require('util')
+const path = require('path')
 const recursiveReadDir = require('recursive-readdir')
 const { getId } = require('./util')
 
@@ -18,6 +19,12 @@ module.exports = function ({ db, config, logger }) {
     mode: 'minimumForPouchDB'
   }))
 
+  app.get('/media/preview/:id', wrap(async (req, res) => {
+    const { previewPath } = await db.get(req.params.id.toUpperCase())
+
+    res.sendFile(path.join(process.cwd(), previewPath))
+  }))
+
   app.get('/cls', wrap(async (req, res) => {
     const { rows } = await db.allDocs({ include_docs: true })
 

src/config.js

@@ -23,6 +23,12 @@ const defaults = {
     width: 256,
     height: -1
   },
+  previews: {
+    enable: false,
+    width: 160,
+    height: -1,
+    bitrate: '40k'
+  },
   isProduction: process.env.NODE_ENV === 'production',
   logger: {
     level: process.env.NODE_ENV === 'production' ? 'info' : 'trace',

src/index.js

@@ -2,6 +2,7 @@ const pino = require('pino')
 const config = require('./config')
 const PouchDB = require('pouchdb-node')
 const scanner = require('./scanner')
+const previews = require('./previews')
 const app = require('./app')
 
 const logger = pino(Object.assign({}, config.logger, {
@@ -16,3 +17,7 @@ logger.info(config)
 
 scanner({ logger, db, config })
 app({ logger, db, PouchDB, config }).listen(config.http.port)
+
+if (config.previews.enable) {
+  previews({ logger, db, config })
+}

src/previews.js

@@ -0,0 +1,91 @@
+const cp = require('child_process')
+const { Observable } = require('@reactivex/rxjs')
+const util = require('util')
+const mkdirp = require('mkdirp-promise')
+const os = require('os')
+const fs = require('fs')
+const path = require('path')
+const { fileExists } = require('./util')
+
+const statAsync = util.promisify(fs.stat)
+const unlinkAsync = util.promisify(fs.unlink)
+const renameAsync = util.promisify(fs.rename)
+
+module.exports = function ({ config, db, logger }) {
+  Observable
+    .create(async o => {
+      db.changes({
+        since: 'now',
+        live: true
+      }).on('change', function (change) {
+        o.next([change.id, change.deleted])
+      }).on('error', function (err) {
+        logger.error({ err })
+      })
+
+      // Queue all for attempting to regenerate previews, if they are needed
+      const { rows } = await db.allDocs()
+      rows.forEach(d => o.next([d.id, false]))
+      logger.info('Queued all for preview validity check')
+    })
+    .concatMap(async ([id, deleted]) => {
+      await generatePreview(id, deleted)
+    })
+    .subscribe()
+
+  async function generatePreview (mediaId, deleted) {
+    try {
+      const destPath = path.join('_previews', mediaId) + '.webm'
+      if (deleted) {
+        await unlinkAsync(destPath)
+        return
+      }
+
+      const doc = await db.get(mediaId)
+      if (doc.previewTime === doc.mediaTime && await fileExists(destPath)) {
+        return
+      }
+
+      const mediaLogger = logger.child({
+        id: mediaId,
+        path: doc.mediaPath
+      })
+
+      const tmpPath = destPath + '.new'
+
+      const args = [
+        // TODO (perf) Low priority process?
+        config.paths.ffmpeg,
+        '-hide_banner',
+        '-i', `"${doc.mediaPath}"`,
+        '-f', 'webm',
+        '-an',
+        '-c:v', 'libvpx',
+        '-b:v', config.previews.bitrate,
+        '-auto-alt-ref', '0',
+        `-vf scale=${config.previews.width}:${config.previews.height}`,
+        '-threads 1',
+        `"${tmpPath}"`
+      ]
+
+      await mkdirp(path.dirname(tmpPath))
+      mediaLogger.info('Starting preview generation')
+      await new Promise((resolve, reject) => {
+        cp.exec(args.join(' '), (err, stdout, stderr) => err ? reject(err) : resolve())
+      })
+
+      const previewStat = await statAsync(tmpPath)
+      doc.previewSize = previewStat.size
+      doc.previewTime = doc.mediaTime
+      doc.previewPath = destPath
+
+      await renameAsync(tmpPath, destPath)
+
+      await db.put(doc)
+
+      mediaLogger.info('Finished preview generation')
+    } catch (err) {
+      logger.error({ err })
+    }
+  }
+}

src/scanner.js

@@ -6,7 +6,7 @@ const mkdirp = require('mkdirp-promise')
 const os = require('os')
 const fs = require('fs')
 const path = require('path')
-const { getId } = require('./util')
+const { getId, fileExists } = require('./util')
 const moment = require('moment')
 
 const statAsync = util.promisify(fs.stat)
@@ -60,15 +60,8 @@ module.exports = function ({ config, db, logger }) {
       })
       await Promise.all(rows.map(async ({ doc }) => {
         try {
-          if (doc.mediaPath.indexOf(config.scanner.paths) === 0) {
-            try {
-              const stat = await statAsync(doc.mediaPath)
-              if (stat.isFile()) {
-                return
-              }
-            } catch (e) {
-              // File not found
-            }
+          if (doc.mediaPath.indexOf(config.scanner.paths) === 0 && await fileExists(doc.mediaPath)) {
+            return
           }
 
           deleted.push({

src/util.js

@@ -1,4 +1,8 @@
 const path = require('path')
+const fs = require('fs')
+const util = require('util')
+
+const statAsync = util.promisify(fs.stat)
 
 module.exports = {
   getId (fileDir, filePath) {
@@ -7,5 +11,17 @@ module.exports = {
       .replace(/\.[^/.]+$/, '')
       .replace(/\\+/g, '/')
       .toUpperCase()
+  },
+
+  async fileExists (destPath) {
+    try {
+      const stat = await statAsync(destPath)
+      if (stat.isFile()) {
+        return true
+      }
+    } catch (e) {
+      // File not found
+    }
+    return false
   }
 }