Created attachment 769516 [details] Bells4.m4a User Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:22.0) Gecko/20100101 Firefox/22.0 (Beta/Release) Build ID: 20130618035212 Steps to reproduce: building intranet website with podcasts - I found directly clicking RSS media links as displayed in FF: 1. mp4 videos play directly in ff 22 on w8 BUT 2. audio only m4a files play back in slow motion Actual results: Clicking the file.mp4 link - a darkened page opens with dark player. Clicking play starts to play the media but the file plays back in slow motion. Expected results: I expected the file to play at normal speed;). I'm an HTML5 newbie. I'm not sure if this is a bug or a feature. I couldn't find any indication of limitations to the AAC files FF can play when searching the web. The file plays correctly in VLC etc. I suppose something about the encoding of the m4a file causes the problem. I tried AddType audio/mp4 m4a .m4a or AddType audio/x-m4a m4a .m4a in .htaccess but this changed nothing. VLC reports the m4a file is AAC SBR+PS, encoded by Lavf53.21.1 I enclose a sample m4a.
A dupe of bug 875644. Thanks for taking the time to report this.