Bug 945513 - Opus-in-WebM tests. r=rillian

detodos.webm was remuxed with ffmpeg N-58726-g9695fb2 from detodos.opus

| + Muxing application: Lavf55.22.100
| + Writing application: Lavf55.22.100
Bug 949525 - VP9 tests. r=cpearce

Remuxed vp9cake.webm to correct CodecDelay values.
Bug 950793 - Loop over all supported codecs in test. r=rillian