[tbb-bugs] #22548 [Applications/Tor Browser]: Firefox downgrades VP9 videos to VP8 when measured performance is not enough

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#22548: Firefox downgrades VP9 videos to VP8 when measured performance is not
enough
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 Reporter:  cypherpunks                          |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:  closed
 Priority:  Medium                               |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:  fixed
 Keywords:  tbb-fingerprinting,                  |  Actual Points:
  TorBrowserTeam201801R                          |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by gk):

 So, the patch in `Benchmark.cpp` does not even compile actually. Here is
 the output with GCC 5.4.0:
 {{{
 /var/tmp/build/firefox-f0b673dbac3a/dom/media/Benchmark.cpp: In static
 member function 'static bool mozilla::VP9Benchmark::IsVP9DecodeFast()':
 /var/tmp/build/firefox-f0b673dbac3a/dom/media/Benchmark.cpp:83:60: error:
 call of overloaded 'GetUint(const char [30], int)' is ambiguous
      Preferences::GetUint("media.benchmark.vp9.threshold", 0);
                                                             ^
 In file included from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dist/include/xpcpublic.h:28:0,
                  from /var/tmp/build/firefox-
 f0b673dbac3a/dom/base/nsJSEnvironment.h:19,
                  from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dist/include/mozilla/dom/CallbackObject.h:31,
                  from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dist/include/mozilla/dom/BindingUtils.h:20,
                  from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dist/include/mozilla/dom/ToJSValue.h:12,
                  from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dist/include/mozilla/dom/IterableIterator.h:34,
                  from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dist/include/mozilla/dom/MediaKeyStatusMapBinding.h:11,
                  from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dist/include/mozilla/CDMCaps.h:18,
                  from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dist/include/mozilla/CDMProxy.h:10,
                  from /var/tmp/build/firefox-
 f0b673dbac3a/dom/media/MediaDecoder.h:11,
                  from /var/tmp/build/firefox-
 f0b673dbac3a/dom/media/ADTSDecoder.h:10,
                  from /var/tmp/build/firefox-
 f0b673dbac3a/dom/media/ADTSDecoder.cpp:7,
                  from /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-
 linux-gnu/dom/media/Unified_cpp_dom_media0.cpp:2:
 /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-linux-
 gnu/dist/include/mozilla/Preferences.h:122:19: note: candidate: static
 uint32_t mozilla::Preferences::GetUint(const char*, uint32_t)
    static uint32_t GetUint(const char* aPref, uint32_t aDefault = 0)
                    ^
 /var/tmp/build/firefox-f0b673dbac3a/obj-x86_64-pc-linux-
 gnu/dist/include/mozilla/Preferences.h:173:19: note: candidate: static
 nsresult mozilla::Preferences::GetUint(const char*, uint32_t*)
    static nsresult GetUint(const char* aPref, uint32_t* aResult)
                    ^
 }}}
 Now, if you look closer at the function in questions you'll see:
 {{{
 uint32_t hadRecentUpdate = Preferences::GetUint(sBenchmarkFpsVersionCheck,
 0U)
 }}}
 And, yes, replacing `0` with `0U` in the patch I merged fixes the
 compilation. I've pushed a fixup commit to `tor-browser-52.6.0esr-8.0-1`
 (commit d93d0469d2b21b67869369063e17074563a49abf).

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22548#comment:22>
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