Audio only stream causes exception in ControlBar.js that prevents playback

[matt-hammond-001]

Environment

• Link to playable MPD file: http://vm2.dashif.org/livesim/testpic_2s/audio.mpd
• Dash.js version: 2.3.0
• Browser name/version: Version 53.0.2785.101 (64-bit)
• OS name/version: Mac OS X 10.11.6

Steps to reproduce

1. Open the v2.3.0 reference player
2. Select an audio only MPD, and click "load" to begin playback

Observed behaviour

DASH stream does not commence playback due to exception raised by ControlBar.js

This appears to be because this line in ControlBar.js uses an if statement that assumes there are both video and audio tracks:

if (availableBitrates.audio.length > 1 || availableBitrates.video.length > 1) {

availableBitrates.video is null, causing the reference to availableBitrates.video.length to raise an exception

Console output

Debug.js:108[10] EME detected on this user agent! (ProtectionModel_21Jan2015) 
Debug.js:108[16] [dash.js 2.3.0] MediaPlayer has been initialized 
Debug.js:108 [2665] Playback Initialized 
Debug.js:108 [3021] Parsing complete: ( xml2json: 2.32ms, objectiron: 0.725ms, total: 0.00305s) 
Debug.js:108 [3022] Manifest has been refreshed at Thu Sep 08 2016 12:31:08 GMT+0100 (BST)[1473334268.555]  
Debug.js:108 [11985] Matching default timing source protocol to manifest protocol:  http://time.akamai.com/?iso 
Debug.js:108 [12041] Local time:      Thu Sep 08 2016 12:31:17 GMT+0100 (BST) 
Debug.js:108 [12042] Server time:     Thu Sep 08 2016 12:31:16 GMT+0100 (BST) 
Debug.js:108 [12042] Difference (ms): -1574 
Debug.js:108 [12046] MediaSource attached to element.  Waiting on open... 
Debug.js:108 [12054] MediaSource is open! 
Debug.js:108 [12054] Duration successfully set to: 1.7976931348623157e+308 
Debug.js:108 [12055] Added 0 inline events 
Debug.js:108 [12056] No video data. 
Debug.js:108 [12056] audio codec: audio/mp4;codecs="mp4a.40.2" 
Debug.js:108 [12066] Schedule controller stopping for audio 
Debug.js:108 [12070] No text data. 
Debug.js:108 [12070] No fragmentedText data. 
Debug.js:108 [12070] No embeddedText data. 
Debug.js:108 [12070] No muxed data. 
    onStreamInitialized @ ControlBar.js:287
    (anonymous function) @ EventBus.js:87
    trigger @ EventBus.js:87
    checkIfInitializationCompleted @ Stream.js:457
    initializeMedia @ Stream.js:437
    activate @ Stream.js:124
    onMediaSourceOpen @ StreamController.js:427

[dsparacio]

Ah darn it!. Ok thanks @matt-hammond-bbc Ill fix today and upload to the public ref player and dev...

[matt-hammond-001]

Thanks for the quick response. These things happen. :)

[dsparacio]

Fixed with PR #1581 - We will update the public ref player with new code as well. Again since in control bar I do not think we need a point release. If the last minute changes continue to crop up with issues we will do a point release. Hopefully this is the last one.