I don't remember the story of the movie. （映画の筋は覚えていない）
日本語で筋と言うときは話の筋のこと。まずは内容＝筋と想定しての言い方です。話の筋はstory またはstory line といいます。
I can't recall what the movie was about（何についての映画だったか思い出せない）
「覚えていない」よりも「思い出せない」の方が近いかなあという場合は
can't remember can't recall などを使います。
movie is about はかなり曖昧に映画のテーマや物語などを指したいときに使えます。英語にもこういう曖昧でおおざっぱな言い方はあるのですが、親しい間柄で使うものであることをお忘れなく。
I don't remember the details of the movie.（映画について詳しいことは覚えていない）
内容だけではなくて、監督や俳優さんなどについても使えます。「細かいこと」を言いたいr時にもこのdetailsを使うことができます。
I don't remember anything about the movie.
その映画について何も覚えていない。
not〜anything：何も〜ない
I don't remember the story of the movie.
その映画のストーリーを覚えていない。
こちらの方が、より具体的に「映画の内容」を示しています。
I think I've seen this movie before but...という前置きをするとFumiyaさんの言いたいニュアンスになるかと思います！参考になさってください★
1. I have forgotten what this movie is about.
私はこの映画が何であるかを忘れてしまった。
2. I don't remember what this movie about.
私はこの映画が何について覚えていない。
Both these statements have the same meaning, that is, that you can't remember what was the
storyline of the movie. The "storyline" of a movie is the story that the movie is trying to tell.
1. I have forgotten what this movie is about.
2. I don't remember what this movie about.
上記の例文はどちらも、映画のstoryline（ストーリー）を思い出せないという同じことを意味しています。映画の"storyline"とはその映画が伝えようとしている内容です。
I saw it so long ago that I don't really remember what it was about.
I can't recall
I don't remember
so long ago - this phrase means that the time was so far in the past
I can't recall - "re" as a prefix means "again" so "re-" "-call" is literally "call again." This word is used to describe the action of remembering the name or definition of something, or bringing something to you mind again.
このフレーズの意味は、ずっと昔の時です。
I can't recall - 接頭辞としての"re"の意味は、"again"（再）ですので、"re-" "-call"は文字通り"call again"（再び呼び起こす）です。 この単語は、何かの名前や定義を思い出したり、誰かのことを思い起こしたりする行為を説明するのに使われます。
To say that you only remember 'bits' of it, is to say that you only can recall certain parts of the movie, and you do not remember the whole story.
The 'plot' of a movie is the story. So to say that you can not remember the plot, is to explain that you have forgotten the story of the film. When we forget things in everyday life, or become confused about things, we can also say "I've lost the plot!", for example:
"I forgot to bring my wallet today and then I thought it was in my pocket but it wasn't, I've lost the plot today!"
only remember 'bits' of itとは、その映画のある一部だけ思い出すことができて、話全てを思い出すことはできないという意味です
映画の 'plot' とは、話のことです。ですので、can not remember the plotとは、その映画の話を忘れてしまったということになります。日常の中で、何かを忘れたり、混乱したときには、"I've lost the plot!"ということもできます。
"I forgot to bring my wallet today and then I thought it was in my pocket but it wasn't, I've lost the plot today!"
今日、財布を持ってくるのを忘れて、ポケットの中にあるかと思ったけど、なかった。やってしまった！
When referring to the "contents" of a movie, in the UK we would call them "scenes".
So you would say something like, "I can't recall any scenes from that movie," or, "I don't remember any part of that movie."
映画の中身について話す時、イギリスでは"scenes"と言います。
ですから"I can't recall any scenes from that movie,"（映画のどのシーンも思い出せない）又は"I don't remember any part of that movie." （あの映画のどの場面も思い出せない）ということが出来ます。
example
"what was the plot about again?".
or
"i can't remember the storyline at all".
or
"i have seen it before, but don't remember the plot".
例
"What was the plot about again?".（あらすじはなんでしたっけ？）
あるいは
"I can't remember the storyline at all".（ストーリーラインを全く覚えていません。）
もしくは
"I have seen it before, but don't remember the plot".（以前に見たことがありますが、あらすじを覚えていません。）
I've seen it, but I can't recall what happened in it.
What is the movie about? I forgot.
"I've seen it, but I can't recall what happened in it"- The word "recall" means that you cannot remember. In this sentence you are saying that you remember that you saw it before, but you do not seem to remember what the plot is of the movie.
" What is the movie about? I forgot."- In this sentence you are stating that you did not merely forget the plot, but you also seemed to have forgotten everything else in the movie.
Thank you for your question, hope this helps!
I know the movie you are talking about but I forget the plot
The title seems very familiar to me but I don't remember what happened during the movie
It is impossible for us to remember everything. We do so many things every day and see many people and watch many movies. It's normal for us only to remember the things that stick out in our mind as important.
We can use these two sentences to tell someone that we can't remember the details of movie we recently saw
I have seen that movie before, but I can't remember the story line.
When you use this sentence you are referring to the fact that you have already seen that particular movie, but you cannot remember that movie very well, you don't remember how that movie unfolds. This could be due to the fact that you haven't seen that movie in a long time.
I've seen it, but I just cannot remember what this movie was about.
I know that I have seen this movie before but I have totally forgotten what happens in it.
When the story line of a movie isn't that memorable then sometimes a person knows that they have seen it but just cannot remember what it was about. Usually, when such a person starts to watch the movie again the memory of the story would come back to them.
It seems vaguely familiar but I can't remember anything
I'm sure I've seen it, but I must have fallen asleep as I can't recall anything
Situations where this word/phrase is used: social, business, formal, informal, when describing experiences, film, memory.
Type of word/phrase: standard language.
Example of this word/phrase:
"I'm sure I've seen it, but I must have fallen asleep as I can't recall anything."
I think I have seen it, but I can't remember what it was about.
I know the film, but I can't remember what happens.
When you have seen a film, play, or read a book, but don't remember what happens, then you can say one of these two sentences.
For example.
Have you ever seen Die Hard?
Yeah, for sure.
What do you think of it?
I would love to tell you, but I can't remember what is was about.
I hope this helps.
Have a great day.
Will.
日本 
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