Ce film est célèbre.

• Ce is used before a masculine singular noun starting with a consonant: ce film, ce livre, ce garçon.
• Cet is used before a masculine singular noun starting with a vowel or silent h: cet homme, cet arbre.
• Cette is used for feminine singular nouns: cette fille, cette voiture.

Since film is masculine and starts with a consonant sound /f/, the correct form is ce film.

Both can translate as “This is a famous film”, but the structure and nuance differ:

• Ce film est célèbre

  • Literally: “This film is famous.”
  • Focuses on the film as a specific, identified thing; you already know which film you’re talking about.

• C’est un film célèbre

  • Literally: “It is a famous film.”
  • More general presentation; often used when introducing or commenting on a film, not necessarily pointing to it physically.

In practice, both are correct; ce film est célèbre sounds a bit more precise about that particular film.

You have two different structures:

1. Subject + être + adjective

   • Ce film est célèbre = This film is famous.
     The adjective célèbre describes the state or quality of the subject via the verb être.

2. Adjective + noun

   • Ce célèbre film = This famous film.
     Here, célèbre is directly modifying the noun inside a noun phrase.

Both are correct, but:

• Ce film est célèbre is a full sentence (with verb).
• Ce célèbre film is a noun phrase, not a standalone sentence.

To say “These films are famous,” you must change all the agreeing words:

• Ce → Ces (plural demonstrative)
• film → films (add -s)
• est → sont (third person singular → plural of être)
• célèbre → célèbres (add -s for plural agreement in writing)

So the plural sentence is:

Ces films sont célèbres.

In writing:

• Masculine singular: célèbre
• Feminine singular: célèbre
• Masculine plural: célèbres
• Feminine plural: célèbres

So the feminine form is spelled the same as the masculine; you only add -s for plural.
In pronunciation, célèbre and célèbres sound the same in everyday speech.

Roughly in IPA: /sə film ɛ selebʁ/

• Ce → /sə/ (like suh)
• film → /film/ (final m is pronounced; it is not nasalized here)
• est → /ɛ/ (like English eh; the st is silent)
• célèbre → /selebʁ/
  
  • stress is usually on the last syllable: se-lè-bre
  • the final -re is pronounced with a French ʁ sound.

There are no liaisons in this short sentence: you say each word separately.

Célèbre generally means “famous, well-known”, like English famous.
Common nuances:

• célèbre: often neutral, can be slightly formal or literary.
• connu: “known, well-known”; sometimes weaker than célèbre.
• populaire: “popular,” emphasizes being liked by many people, not just known.

For a movie, célèbre is natural and common: un film célèbre, ce film est célèbre.

Yes:

• Ce film est très célèbre. → This film is very famous.
• Ce film est bien connu. → This film is well known.

très célèbre intensifies the idea of fame;
bien connu is slightly more informal and means “widely known,” sometimes with a nuance of “everybody knows it.”

Est is the third person singular form of être used with singular subjects:

• il/elle/on est, le film est, ce film est

Sont is the third person plural form, used with plural subjects:

• ils/elles sont, les films sont, ces films sont

Since film is singular, you must use est: Ce film est célèbre.

Yes, but the meaning changes slightly:

• Ce film est célèbre. → This / That film is famous.
  You’re pointing to or clearly identifying a particular film.

• Le film est célèbre. → The film is famous.
  More neutral; it assumes the listener already knows which film you mean from context.

Both are grammatically correct; ce is more demonstrative than le.

In French, you cannot normally drop the determiner (article or demonstrative) before a singular countable noun. You must use something like:

• un film (a film)
• le film (the film)
• ce film (this/that film)

So Film est célèbre is ungrammatical.
You need Ce to make a correct noun phrase: Ce film est célèbre.