Allan is quite right - the only (basic) answer you will get to this from anyone working within the industry as actor, casting director, agent etc. is 'No, no, no, no, no!'.
I don't wish this to belittle the quality of any supporting work you tend to do on a regular basis (if that's the case) - the industry standard is simply to draw up a separate CV for your work as a walk-on artist and use this to generate further commissions in the walk-on field for yourself, whilst keeping your straight acting CV distinct. This actually tends to make you seem more professionally minded on both sides - not only those casting acting roles, but those who are promoting you for walk-on work appreciate the distinction, because they are all in the game of making sure that they provide the most appropriate sounding services to those who ask for their expertise.
If you have just done the odd walk - on or two for experiences' sake, and would like to place it on the CV to bulk it up, the general advice is not to bother - it is difficult to make an 'extra' part look impressive to those with an eye for detail, who may examine your CV - though the temptation is often because these credits can link you to more 'high profile' productions than some of the other work you pick up, to list the casting. But a distinction is drawn by casting directors between roles you have had to audition for, and those that were just allowed you 'on spec' (which is how most walk on casting works).
There is certainly a thin line, where an actor can take on scenes which amount to a very small number of lines or airtime in a screen project, but still gain a credit - essentially any character identified in the script, who is given dialogue, will ultimately end up in the cast list, however, and is considered 'cast'. Equally, some characters are quite sizeable parts (I have played some myself), but sound curiously minor because they aren't technically named as such - many is the low budget in which the main leads are called e.g. 'Man' or 'Woman', which doesn't always read impressively on the CV! - still, you should always that the character was a significant, identifiable part before listing it.
Interestingly, 'extras' parts are sometimes listed more easily on resources like IMDB, and this seems to be held to be less of an issue (perhaps because IMDB serves as a database of record, and is not considered to be your 'personal application' for a job), but even these tend to be subject to the production company's confirmation - once again, many minor sounding parts - 'First Security Officer', 'Main Henchman' etc. were referenced in the shooting script and given at least one line in formalised dialogue and so read as 'cast' - many walk on roles are listed as 'uncredited', which gives the immediate clue to the fact that the 'role' was, in fact, support work.
Things like work in music videos and commercials are often a grey area, it must be said, because frequently these jobs pay well, and may even be actively got for you by an agent, but may not require much more of you than the ability to perform like an extra on set (some, it is true, demand much more extensive acting, and, in essence, feature you in 'lead' parts). With these, I think the judgement call has to be whether you feel yourself that your involvement with the project constituted a substantial role or not.
Very occasionally, also, you can do a walk on role that may be promoted to a more significant status within the film, TV show, commercial than was initially envisaged - this *may* be worth listing if you know for a fact that you were given some decent screen time or even a line or two in doing it - though you may not receive an end credit in the long run, and would (presumably) be IMDB listed as 'uncredited'.
Hope that's useful advice - the division is not *always* as clear cut as we'd like - but, when in doubt, leave it out!
