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Mobile Video Interaction

May 21, 2019 • Manuel

Mobile records vs Browser records

This is the second special case that ELAT had to tackle, and it was caused by the introduction of the edX mobile app, which changed the structure of video related records compared to the browser video records. Discovered and fixed 21/05/2019

This is how a pause_video record looks like:

{
  "accept_language": "en-IN",
  "agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.79 Safari/537.36 Edge/14.14393",
  "context": {
    "course_id": "course-v1:DelftX+EX101x+3T2016",
    "org_id": "DelftX",
    "path": "/event",
    "user_id": 888888
  },
  "event": "{\"code\": \"zppgbNoqBBI\", \"id\": \"ba666985e20d4eb18e593461c28790c0\", \"currentTime\": 303.9990418602173}",
  "event_source": "browser",
  "event_type": "pause_video",
  "host": "courses.edx.org",
  "ip": "N.N.N.N",
  "name": "pause_video",
  "page": "https://courses.edx.org/courses/course-v1:DelftX+EX101x+3T2016/courseware/153c585b5fc643008fafb60c35aaa575/9070b59046dc453998e33b2ccf344ff5/?child=first",
  "referer": "https://courses.edx.org/courses/course-v1:DelftX+EX101x+3T2016/courseware/153c585b5fc643008fafb60c35aaa575/9070b59046dc453998e33b2ccf344ff5/?child=first",
  "session": "8940f3610cfb8825b7a7cd6b85bfa52f",
  "time": "2016-12-16T01:43:57.340314+00:00",
  "username": "AAAAAA"
}

This is another pause_video record:

{
  "accept_language": "",
  "agent": "Dalvik/2.1.0 (Linux; U; Android 6.0.1; SM-N920C Build/MMB29K)",
  "context": {
    "application": {
      "name": "edx.mobileapp.android",
      "version": "2.7.5"
    },
    "client": {
      "app": {
        "build": 2007005,
        "name": "edX",
        "namespace": "org.edx.mobile",
        "version": "2.7.5"
      },
      "device": {
        "adTrackingEnabled": false,
        "advertisingId": "ad_id",
        "id": "hex_id",
        "manufacturer": "samsung",
        "model": "SM-N920C",
        "name": "noblelte",
        "type": "android"
      },
      "ip": "N.N.N.N",
      "library": {
        "name": "analytics-android",
        "version": "3.4.0"
      },
      "locale": "en-GB",
      "network": {
        "bluetooth": false,
        "carrier": "STC",
        "cellular": false,
        "wifi": true
      },
      "os": {
        "name": "Android",
        "version": "6.0.1"
      },
      "screen": {
        "density": 3.5,
        "height": 2560,
        "width": 1440
      },
      "timezone": "X/X"
    },
    "component": "videoplayer",
    "course_id": "course-v1:DelftX+EX101x+3T2016",
    "org_id": "DelftX",
    "path": "/segmentio/event",
    "received_at": "2017-02-09T07:39:17.857000+00:00",
    "user_id": 999999
  },
  "event": {
    "code": "mobile",
    "currentTime": 33.751,
    "id": "event_id"
  },
  "event_source": "mobile",
  "event_type": "pause_video",
  "host": "courses.edx.org",
  "ip": "",
  "name": "edx.video.paused",
  "page": "https://courses.edx.org/xblock",
  "referer": "",
  "session": "",
  "time": "2017-02-09T07:38:48.857000+00:00",
  "username": "XXXXXXXX"
}

The records look pretty different, and that is because the second one is for a student using the edX mobile app, which apparently can track much more information about the device being used to interact with the video. The important difference, however, is in the event field of both records, since ELAT uses this to find the id of the video and process the session of a student interacting with that particular video. This is how it looks in the browser record (which was the type of record used to develop ELAT):

 "event": "{\"code\": \"zppgbNoqBBI\", \"id\": \"ba666985e20d4eb18e593461c28790c0\", \"currentTime\": 303.9990418602173}"

While for the mobile record, it looks like this:

"event": {
  "code": "mobile",
  "currentTime": 33.751,
  "id": "39b0ffc9bfab486fa9ab479f64d730b3"
}

In the first one, the whole value for the event field is a string, not a JSON object, therefore the
quotes are being “escaped” by adding a backslash like this \ in front of them. To process this values, ELAT had to read this string and parse it again to create a new “mini-object” for the event, and then read the values of each field. The second one is a normal nested JSON object (check the context field of both records, those are nested JSON objects), so the quotes do not have to be escaped.

Discovery

As we tested ELAT on newer courses (read: with mobile viewing records) some course interaction entries were being processed with no video_id, which raised an error in the database, because it is a required field. Then it was a matter of diving into log files, searching for the user id and date of those video interactions to find that those records did have a video id, but in different format.

Fix

We may never find out why it was recorded as a string in the browser records, but as an object in the mobile app, all we know is that ELAT has to identify video records from a mobile application and process them differently than the browser records.