Most UK mainline trains nowadays are air conditioned and have sealed windows, but there are still a few which have opening vestibule windows. The possibility of much more interesting views with the lens just out of the window therefore still exists.

Leaving aside all the other health and safety considerations, is it possible that the internal mic in the camera could be damaged by the buffeting wind? Specifically, is there a safe speed beyond which the rapidly changing pressure levels could cause damage? Obviously, it is not intended to actually use the built in mic to acquire audio under these conditions nor would an external mic be attached to the camera!

For example, a certain world famous railway feature not very far away from me has a max. line speed of 50 mph, which could ruin your hairdo, but is otherwise not too much of a problem. However, further south on the same route line speeds increase to 125 mph. Would that be a potential problem for sound pressure levels round a mic which is built in to the camera body?

Apart from anything it will sound dreadful so why try to record sound in that way as you have already realised, what you need is a dynamic mic preferably an omni mic with a wind protector on it, you can then cover up the camera mic to protect it from any harm.

I doubt if the wind will damage the camera mic but as said you need top think about what sound you wish to get for the completed shots.

I did a similar thing as a test with a canon HF11 clamped onto the passenger window of my car but the sound was totally un-useable as the wind buffeting was just too much for the sensitive electret condensor mics.

Thanks Gary. The sound acquired with the video is done with a mic well inside the train, connected by cable or radio. The final audio will have a voiceover as well.

The idea of covering up the camera mic to protect it seems sensible - maybe I should just cover it with a piece of gaffer tape. When I first realised that there were still opening windows on the HST, I didn't have time to rig anything up. Next time I can be prepared.

I don't know what camera you have, or what type of mic is built into it, but if its a dynamic mic there should be no issue with the wind damaging it. If it's a condenser mic, then you might have a problem. The element in these mics is a few millimeters thick Mylar membrane. Any excessive pressure could conceivably tear the membrane, I would think. I have no idea at what wind speed such damage would occur. Tape over the mic and keep it safe, would be the best bet.