Bug 188068 – Safari HLS playback ignores DEFAULT attribute for audio tracks, selects first listed in manifest

• Status: NEW
• Component: Media

[Garrett Singer]

With Safari's native HLS playback, if a master manifest contains demuxed audio and video, Safari will ignore the DEFAULT attribute on audio tracks and instead start playback with the first listed track.

This can be seen with the following manifest: http://d2zihajmogu5jn.cloudfront.net/elephantsdream/hls/ed_hd_ad.m3u8

Steps to Reproduce:
1) Create a simple video player on a page, e.g.,

<video controls>
  <source src="http://d2zihajmogu5jn.cloudfront.net/elephantsdream/hls/ed_hd_ad.m3u8" type="application/x-mpegURL" />
</video>

2) Load the page in Safari and play the video

Expected Behavior:

If the audio group with ID "ed_audio_64k" is chosen, then the track with NAME="Main" should be chosen, as it has DEFAULT=YES.

Seen Behavior:

The audio group with ID "ed_audio_64k" is chosen, but the first listed track, with NAME="Audio Described" is chosen, even though it has DEFAULT=NO.

Other observations:

We've also seen this behavior when the AUTOSELECT attributes were removed, and we've seen it with and without CHARACTERISTICS="public.accessibility.describes-video" added to to the described audio track.

The first track listed in the manifest is always chosen.

Although the HLS specification says that the DEFAULT attribute only "SHOULD" be considered, in the absence of other hints from the manifest or gleaned by the player, the DEFAULT attribute should probably be considered and the track with YES chosen over the track with NO, regardless of order.

Please let me know if you need any more information, and thank you.

[Radar WebKit Bug Importer]

<rdar://problem/42668396>