Not all playback issues result in onPlayBackError callback

Describe the bug

In some cases it is possible for playback to fail without the add-on being able to report back to the user. The user will simply see a busy state followed by nothing because the add-on does not know playback has failed.

The normal flow is that Kodi or InputStream Adaptive performs an xbmc.Player.onPlayBackError callback so the add-on can handle it as expected (i.e. try an alternative playback method like use HLS instead of MPD, or provide a specific error to the user).

Here is an example of this problem:

2020-04-10 02:12:52.074 T:1378874240  NOTICE: [plugin.video.vrt.nu] Access: plugin://plugin.video.vrt.nu/play/id/vid-84618801-4e10-46a2-9403-d444fce53630/pbs-pub-0738b2b8-4242-4783-9686-8edb3f66be79
2020-04-10 02:12:52.106 T:1378874240  NOTICE: [plugin.video.vrt.nu] Got cached token '/storage/.kodi/userdata/addon_data/plugin.video.vrt.nu/tokens/ondemand_vrtPlayerToken.tkn'
2020-04-10 02:12:52.110 T:1378874240  NOTICE: [plugin.video.vrt.nu] URL get: https://media-services-public.vrt.be/vualto-video-aggregator-web/rest/external/v1/videos/pbs-pub-0738b2b8-4242-4783-9686-8edb3f66be79$vid-84618801-4e10-46a2-9403-d444fce53630?vrtPlayerToken=b10@e5af19407961d59b683f1b2c7384165485b11852a527bf030d3c1dd0f940cca3&client=vrtvideo@PROD
2020-04-10 02:12:52.487 T:1378874240  NOTICE: [plugin.video.vrt.nu] Protocol: mpeg_dash
2020-04-10 02:12:52.700 T:1378874240  NOTICE: [plugin.video.vrt.nu] Play: https://ondemand-cf.lwc.vrtcdn.be/content/vod/vid-84618801-4e10-46a2-9403-d444fce53630-CDN_5/vid-84618801-4e10-46a2-9403-d444fce53630-CDN_5_nodrm_90b2af9a-63cf-478e-b20b-46e7aec0c0cb.ism/.mpd
2020-04-10 02:12:52.730 T:1937706416  NOTICE: VideoPlayer::OpenFile: plugin://plugin.video.vrt.nu/play/id/vid-84618801-4e10-46a2-9403-d444fce53630/pbs-pub-0738b2b8-4242-4783-9686-8edb3f66be79
2020-04-10 02:12:52.736 T:1432351616  NOTICE: Creating InputStream
2020-04-10 02:12:52.761 T:1465889664  NOTICE: [plugin.video.vrt.nu] [PlayerInfo 9559] Event onPlayBackStarted
2020-04-10 02:12:52.764 T:1465889664  NOTICE: [plugin.video.vrt.nu] URL get: https://vrtnu-api.vrt.be/search?i=video&facets[videoId]=vid-84618801-4e10-46a2-9403-d444fce53630&size=1
2020-04-10 02:12:53.323 T:1432351616   ERROR: CCurlFile::FillBuffer - Failed: HTTP returned error 415
2020-04-10 02:12:53.323 T:1432351616   ERROR: CCurlFile::Open failed with code 415 for https://ondemand-cf.lwc.vrtcdn.be/content/vod/vid-84618801-4e10-46a2-9403-d444fce53630-CDN_5/vid-84618801-4e10-46a2-9403-d444fce53630-CDN_5_nodrm_90b2af9a-63cf-478e-b20b-46e7aec0c0cb.ism/.mpd:
2020-04-10 02:12:53.323 T:1432351616   ERROR: AddOnLog: InputStream Adaptive: Cannot download https://ondemand-cf.lwc.vrtcdn.be/content/vod/vid-84618801-4e10-46a2-9403-d444fce53630-CDN_5/vid-84618801-4e10-46a2-9403-d444fce53630-CDN_5_nodrm_90b2af9a-63cf-478e-b20b-46e7aec0c0cb.ism/.mpd
2020-04-10 02:12:53.323 T:1432351616   ERROR: AddOnLog: InputStream Adaptive: Could not open / parse mpdURL (https://ondemand-cf.lwc.vrtcdn.be/content/vod/vid-84618801-4e10-46a2-9403-d444fce53630-CDN_5/vid-84618801-4e10-46a2-9403-d444fce53630-CDN_5_nodrm_90b2af9a-63cf-478e-b20b-46e7aec0c0cb.ism/.mpd)
2020-04-10 02:12:53.324 T:1432351616   ERROR: CVideoPlayer::OpenInputStream - error opening [plugin://plugin.video.vrt.nu/play/id/vid-84618801-4e10-46a2-9403-d444fce53630/pbs-pub-0738b2b8-4242-4783-9686-8edb3f66be79]
2020-04-10 02:12:53.324 T:1432351616  NOTICE: CVideoPlayer::OnExit()
2020-04-10 02:12:53.382 T:1937706416  NOTICE: CVideoPlayer::CloseFile()
2020-04-10 02:12:53.383 T:1937706416  NOTICE: VideoPlayer: waiting for threads to exit
2020-04-10 02:12:53.383 T:1937706416  NOTICE: VideoPlayer: finished waiting
2020-04-10 02:12:53.403 T:1465889664  NOTICE: [plugin.video.vrt.nu] [PlayerInfo 9559] Event onPlayBackStopped

IIRC this also happens on Widevine playback issues where inputstreamhelper cannot offer to install the Widevine library when playback fails because we do not know. If we did (e.g. through onPlayBackError) we would not have to check everything beforehand everytime. See emilsvennesson/script.module.inputstreamhelper#69

This relates to: #307

To Reproduce

Steps to reproduce the behavior:

1. Make it fail in a specific way :-)

Expected behavior

We should get an xbmc.Player.onPlayBackError call.

Additional context

• Operating system: LibreELEC v9.2.1
• Kodi version: 18.6
• Addon version: 2.3.2
• Using a VPN: no
• Country you are using the addon from: BE

Start by tracing the xbmc.Player.onPlayBackError and onPlayBackStopped entry points around the logged InputStream Adaptive MPD failure, and compare this with the Widevine case referenced through inputstreamhelper#69. Reproduce a playback failure if possible and determine whether the add-on receives an error callback instead of only the stopped event; related issue #307 provides additional context.