[theora] ffmpeg2theora 0.25 : This doesn't look like a Speex file

[ogg.k.ogg.k at googlemail.com]

libspeex writes "This doesn't look like a Speex file" when passed a
header packet which isn't actually one (eg, when one tries to probe
for Speexiness).
It doesn't in itself mean that something is wrong, just that the data
probed isn't Speex.