Comment 6 for bug 1301341

More info from Chris:

<oSoMoN> chrisccoulson, what would it take to enable support for mp3 for the audio tag by default in oxide?
<chrisccoulson> oSoMoN, basically, we need 2 build steps (the current one and one with proprietary_codecs=1), so that libffmpeg can be built twice
<chrisccoulson> the chromium source package does something like this, but it actually gets it a bit wrong (it breaks incremental builds for some reason)
<chrisccoulson> i think because it reconfigures gyp after building chromium to build ffmpegsumo a second time with h264/mp3