The university may want independent evidence of what took place.
These notes represent my own views. I am not a lawyer and readers must exercise their own judgment.
Some consideration of this topic is now unavoidable because University of Bristol is more frequently asking for independent evidence of events, rather than just taking one person’s word for what happened.
It's fairly easy to collect basic evidence with a smart phone, though there are some limitations and potential pitfalls.
A few minutes of video of the general scene will establish the location, the time and date, and possibly some general outlines of the event: eg, there are swirling disco lights, there are people in the garden or outside at the front of the house, there are a lot of people arriving and getting out of taxis, windows and doors are open, etc. The audio track may help establish the basic components of the disturbance: beat music, noise from a large outdoor gathering of people, shouting, singing, and so on.
In general, this basic evidence ought to be enough to corroborate your written description of the event if you submit a noise complaint. If you make more-specific allegations, eg that a particular person deliberately damaged a parked car, the need for evidence will be that much greater (and some of the pitfalls might be bigger). My comments are concerned with the general scenario rather than something very specific.
Smart-phone microphones don’t accurately depict party noise: They tend to downplay low-frequency beat music and highlight human voices. So the recording may establish that both kinds of noise are present, but not their relative contribution. This ought to be sufficient for the purposes of making a complaint (you are not likely to be asked to prove a particular decibel level), but it is nevertheless worth commenting when you submit the evidence that while it records different types of noise, it may not be accurate as to levels.
For reasons related to the further comments below, you are likely to be restricted in what you can see and are able to capture on video. If you are viewing the property from the street, you probably cannot see into the garden, which may be where the main activity is taking place. The video will nevertheless probably establish that something is happening at that address, and that might be enough.
Taking video in full view of the event’s participants may be seen by them as provocative, and could compromise your safety. It’s better to record from within your own property if possible (and, again, without needlessly attracting attention to the fact you are doing it).
Taking video without permission could entangle you in data-privacy arguments. My view (untested) is that you ought to be on reasonably safe ground if you are taking general pictures of the scene from your own property, or from the public road or pavement, with the intention of capturing the impact of events on you (or recording crime) for the purposes of making a complaint. From distance, at night, individuals are unlikely to be identifiable (which for these purposes is preferred). If you take close-ups of recognisable people and then post them on social media you are more likely to face counter-claims about privacy violation. (You might be surprised how vociferously people who are keeping the neighbourhood awake feel entitled to defend their privacy, with no notable trace of irony.)
The difficulties mentioned underline that the best “evidence” may well be the corroborating testimony of one or more neighbours who can independently confirm what happened. As I've suggested elsewhere, if you live in an area with a lot of students and anticipate that you might need to make a complaint at some point, it's useful to form a WhatsApp group with your neighbours so you can support each other. That can include the neighbours living at the back, who can see the garden that you can't.
A practical problem is that most of these events are taking place at night and the scene may not be well illuminated. Check if your smart phone has a night-camera mode. If not, the NightCap camera app, available for both iPhone and Android, is one of several apps available that will enhance the incoming light to make clearer pictures or video, provided you give it a few seconds to adjust to the ambient light level. (I have used this app: it works.) https://www.nightcapcamera.com/
It can also be useful if your video displays the time and date (and possibly also the address) at which it was taken, and there are apps that do this, too. Except that (a) they don’t work with NightCap and (b) the timestamp is editable, just like the information your phone records when you capture a video or photo. So it’s not actually proof of the time and date the images were captured. The only way I can think to do that—if it really matters—is to take the video, then immediately email it to yourself or the university. The time and date of the email (which so far as I know can’t be changed) will then evidence the creation of the images.
Another app you might consider is the Noise App. The main idea behind this is that you make recordings in your own home, then send them to an account provided by your local council, whose officers will review the files. (See Repeat disturbances.) However, to access the Bristol CC account you will have to have been accepted as a client, having made a noise complaint in the normal way. But you can download the app, then pay £3 to create a personal account that allows up to 10 recordings. Once made, they can be shared with others (eg, the university), and they are time-stamped. In this case, the information appears not to be editable, so does evidence the date, time and location. https://v2.thenoiseapp.com/