This question was asked by a legal of mine. There was a criminal case and a recording. The recording was made indoors by a surveillance camera. The problem was that the room was too dark. For this reason it was desirable to get a more detailed recording and I was asked if it is possible.
First of all there is no simple answer to this question. It depends on what you need to improve.
The video recording in fact is a sequence of frames, and every frame is like a photo. Every camera has technical specs and one of them is FPS(Frames per Second). This is the number of frames the device is able to produce per second. However “is able” does not always mean that it does. For sample, if you have a camera with 30 FPS it is still could be configured to produce just 15 FPS. Obviously 15 frames takes less disk space than 30 frames do, but have lower quality also. There is no way to raise quality of recording by increasing number of frames: if you have 15 photos, you can copy each of them, but number of useful information will not grow.
At the same time it may help to play video in slow motion. The higher FPS you have, the more useful it could be.
In case we have a black/white videofile, there is no way to make it color.
What if there was not enough lite? Is it possible to make image more clear? Generally, camera should automatically adjust brightens depending on light level. That means that most probably you’ll be able to increase brightness by simply increasing brightens of your monitor. Re-encoding of digital video recording most probably will not give a better result.
And the last thing it is possible to do is to ask an expert to see at the recording. And eye of professional may recognize something that is not visible to amateurs.