I'm trying to use mencoder to capture tv using bktr(4).  The video
part works fine, but the audio is failing horribly.

The capture loop of mencoder wants to know ahead of time how many
bytes of audio data will be read from the device, so it can allocate
packet buffers of the right size before reading.  It calls ioctl
FIONREAD to learn this.

Our audio device doesn't implement this ioctl.  Doing so looks like
it could be tricky in the face of the potential rate conversion
the driver might do in some cases, there's a lot of code in the
read path.

I'm after suggestions from the audio experts as to the best way to
get hold of the relevant information - either to implement FIONREAD,
or to change mencoder to find it another way.

--
Dan.