[tbb-bugs] #29859 [Applications/Tor Browser]: Playing videos on Twitter is not working and freezing the mobile browser

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#29859: Playing videos on Twitter is not working and freezing the mobile browser
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 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:
                                                 |  needs_review
 Priority:  High                                 |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tbb-mobile, GeorgKoppen201904,       |  Actual Points:
  TorBrowserTeam201904R, tbb-8.5-must            |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by gk):

 Okay, so, if we really can't handle HLS, be it on desktop or mobile we get
 the options to download the m3u8 file and/or open it with an external app.
 One can test that behavior with

 https://azure.microsoft.com/en-us/blog/live-247-reference-streams-
 available/

 On mobile with 8.5a10 the symptoms of this bug are visible but with my
 patch one gets the desktop behavior of the external helper app dialog
 showing up. Now, why can videos on Twitter still be played?

 If there is no HSL player available you'll see something like
 {{{
 [2386:Main Thread]: D/nsMediaElement 0x61a00026a080
 CanPlayType(application/x-mpegURL) = ""
 [04-01 15:23:14] Torbutton INFO: tor SOCKS:
 https://abs.twimg.com/k/en/15.hls11.en.7d01861d350d623607c9.js via
                        twitter.com:f6ce0dc9bc9687a8480179a1e5b8b7b7
 }}}
 in your logs. The first line is interesting because it shows that the
 browser is not falling back to something else via
 `DecoderTraits::CanHandleMIMEType`, because there is the empty string
 after the "=", which boils down to `CANPLAY_NO` (via
 `HTMLMediaElement::GetCanPlay()` either because `!containerType` or
 because `DecoderTraits::CanHandleConteinerType` gave it back (which itself
 called
 `CanHandleMediaType` for the check)).

 The second line is interesting because it shows that the HLS support is
 provided by Twitter via some JS file which explains why the content (both
 on desktop and mobile) is playing at all. How frequent that fallback
 mechanism is on the web I don't know but either way, I think we can live
 with the patch for now.

 Once this is fixed I'll open a follow-up bug for properly enabling HLS
 support again.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29859#comment:12>
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