There is no fixed-point vorbis encoder (see bug 932390) so currently we cannot write baseline WebM files on mobile. Including libvorbisenc in mobile builds would resolve this, and would be better than not writing WebM even though it will be slow on handsets with no or poor FPU. In the long term we prefer Opus audio in WebM, but this can be useful until that sees more adoption. There maybe some issues with symbol collision and the libtremor fixed-point _decoder_ for vorbis, which we must continue to use.

Ralph - is this still relevant and important to do? What major browsers/OSes don't support Opus in WebM's?

Good point. I think we can close. I believe the Android system supports ogg vorbis, but not opus, prior to 5.0 (and maybe only in webm/matroska). https://developer.android.com/guide/appendix/media-formats.html Both firefox and chrome support it, and edge plans to implement opus before vorbis. https://dev.windows.com/en-us/microsoft-edge/platform/status/opusaudiocodec