AVPlayer on iOS 11 and tvOS 11 hangs when playing HLS video with empty VTT segments

Number:rdar://452145416 Date Originated:5 Oct 2017
Status:Open Resolved:
Product:iOS and tvOS Product Version:11
Classification:Bug Reproducible:Always
AVFoundation (AVPlayer)

AVPlayer on iOS 11 and tvOS 11 hangs when playing HLS video with empty VTT subtitle segments. This should be legal according to Pantos Draft RFC (3.5.) stating that: "A WebVTT Segment MAY
   contain no cues; this indicates that no subtitles are to be displayed
   during that period."

Steps to Reproduce:
Play the following HLS video using AVPlayer either in iOS 11 or tvOS 11:

With subtitling enabled, the playback will stall. Without subtitles, playback will work as expected. On previous iOS and tvOS the video will play as expected in both cases.

Expected Results:
Video should play without hanging.

Actual Results:
The following message is found in AVPlayer errorLog, although playerItem status does not change to AVPlayerItemStatusFailed.

#Software: AppleCoreMedia/ (Apple TV; U; CPU OS 11_0 like Mac OS X; en_us)
#Date: 2017/10/05 08:24:32.032
#Fields: date time uri cs-guid s-ip status domain comment cs-iftype
2017/10/05 08:24:32.032 https://cdnsecakmi.kaltura.com/api_v3/index.php/service/caption_captionasset/action/serveWebVTT/captionAssetId/0_tkxcudz8/ks/djJ8MTk1Njc5MXxbHYJlFnvUfDZK-eyg0CdAWrFtes9UkBJCFeSV2cJTsTpDO224Y2FmpiiBp5GjaOyZsGM2HqKsfAJEiP1wBlm0nv9laLV2zgIt4XBlt927lE3BmXj2xXDVLxGEvm1K2gxnOpVP3EQFHTkxqflerhHUcRTAta1rKIjPnFkfY1JbUXC9IldWNm8eyEMY_tuNvLj8ncHKBT_6mspHZDaNtvvxlZSxIyAK9FMy1Rzat1hm2NL2zMTUrzOLyRCxGV2nbut_LUHrSxuqqxYAfMDuBjsF/version/2/segmentIndex/1.vtt 95D71C2D-8446-4F7C-813C-C8C82B795662 -12318 "CoreMediaErrorDomain" "Segment exceeds specified bandwidth for variant" -

XCode 9 (9A235)

XCode 9.0 (9A235)
iOS 11  and tvOS 11 (simulator and Apple TV 4).


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