A video was made of a so called crime by a wired informant. The police officer showed the video to a friend of his before an arrest was ever made . Is this legal?

It may not be illegal. It depends on the friend's connection with the case. It depends on whether the privacy of someone was violated.

However, it could cause trouble for the officer.

More info would be needed, if the friend, took possession of the video that was given back to the officer and then it was entered into evidence, it may be a reason to have it thrown out.

So how it was shown, and more is needed

The person that the video was shown to called and said it was shown to the firemen at the station he worked at as a training tape but I had an attorney that knows the fire chief and he said that that was not true,they only shoe videos that come from a video bank in California,never from the area that they are made in. The video was shown in mid March and arrest was not made until July 14.

So what is your part in this? And, most importantly, does the showing compromise the case.