I was in a mood.
Maria2

"I was in a mood" such as in the subtitling in the video means:
"I was unhappy"
"I was angry"
"I was cross"
"I got annoyed" or "I was annoyed"
He was or became unhappy/angry/cross/annoyed
A sentence in context:
It's best just leave him on his own when he's in a mood.
j33

I associate it with being in a negative mood -- like "I was (feeling) moody". Also, I think it's quite an informal way of speaking.
I wouldn't recommend people learning English to use this phrase because it's quite confusing and people might think you were making a mistake with your speech.
MarkE

I would say in general it's a negative mood.
Mycroft

It really depends on context.
I was in a/the mood to do the project. (I felt like doing the project.)
I was in a/the mood to lay around the house all day. (I felt like laying around the house all day.)
”Why did you kill that guy?”
”I was in a mood. (to do it)”
[RussianInput]

To be 'in a mood' means you were annoyed, pissed off, sulking, grumpy.
cheska99

Mycroft is right. There are at least two senses for "in a mood," and it c an be both positive and negative if it's "I'm in a mood to do something." 'I was in a mood," can be both positive and negative, but is more usually negative.
MarkE

To say "I was in a mood" at least in my mind would never be a positive thing.
It would sound so strange to hear someone say "I was in a mood" and they be referring to something positive. At least that's how I have always perceived this.
[RussianInput]

Nah, you don't say 'i'm in a mood to do sth'. 'In a mood' is a set phrase which means to be annoyed or <insert synonym here>.