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Cannot play mp4 files

  • 5 replies
  • 2 have this problem
  • Last reply by FredMcD

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On Windows Vista, firefox 38.0.5 cannot play mp4 files. Both MPC-HC and Windows Media Player can play mp4 files. I have ffdshow installed.

These are enabled:

Results from show:

Disabled: H.264, MSE & H.264, MSE & WebM VP9

Enabled: HTMLVideoElement, Media Source Extensions, WebM VP8

Youtube videos are also locked at 360p using the html5 player.

OGG / WebM files play fine.

Modified by chuck1899

All Replies (5)

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Can anyone help?

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You can check these media prefs on the about:config page:

  • media.directshow.enabled
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They are both enabled.

Refresh Firefox - reset add-ons and settings Refreshing Firefox didn't seem to do anything either.

Modified by chuck1899

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It's been a month and even with Firefox 40.0.3 it still doesn't work.


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Sometimes, messages get lost from inactivity. Sorry.

check this:

  • see if there are updates for your graphics drive drivers

  • disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)

  • disable hardware acceleration in the Flash plugin See also: