fix(Google Gemini Node): Determine the file extention from MIME type for image and video operations

[RomanDavydchuk]

Summary

Google Gemini node currently always uses png as the file extension for images that are generated/edited and mp4 for generated videos. This causes issues when the actual image/video is not png or mp4. This PR fixes that by determining the file extension based on the file's MIME type

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/NODE-4708/community-issue-google-gemini-node-mismatch-between-mimetype-imagejpeg
Closes #27382

Review / Merge checklist

• I have seen this code, I have run this code, and I take responsibility for this code.
• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with Backport to Beta, Backport to Stable, or Backport to v1 (if the PR is an urgent fix that needs to be backported)

[github-actions]

Performance Comparison

Comparing current → latest master → 14-day baseline

Idle baseline with Instance AI module loaded

Metric	Current	Latest Master	Baseline (avg)	vs Master	vs Baseline	Status
instance-ai-heap-used-baseline	186.29 MB	186.29 MB	186.40 MB (σ 0.27)	+0.0%	-0.1%	✅
instance-ai-rss-baseline	342.32 MB	342.32 MB	362.79 MB (σ 23.42)	+0.0%	-5.6%	✅

docker-stats

Metric	Current	Latest Master	Baseline (avg)	vs Master	vs Baseline	Status
docker-image-size-runners	386.00 MB	386.00 MB	391.20 MB (σ 9.93)	+0.0%	-1.3%	✅
docker-image-size-n8n	1269.76 MB	1269.76 MB	1269.76 MB (σ 0.00)	+0.0%	+0.0%	—

Memory consumption baseline with starter plan resources

Metric	Current	Latest Master	Baseline (avg)	vs Master	vs Baseline	Status
memory-heap-used-baseline	114.77 MB	114.54 MB	114.20 MB (σ 0.47)	+0.2%	+0.5%	⚠️
memory-rss-baseline	290.41 MB	332.36 MB	290.22 MB (σ 47.80)	-12.6%	+0.1%	✅

How to read this table

• Current: This PR's value (or latest master if PR perf tests haven't run)
• Latest Master: Most recent nightly master measurement
• Baseline: Rolling 14-day average from master
• vs Master: PR impact (current vs latest master)
• vs Baseline: Drift from baseline (current vs rolling avg)
• Status: ✅ within 1σ | ⚠️ 1-2σ | 🔴 >2σ regression

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[cubic-dev-ai]

No issues found across 8 files

Architecture diagram

sequenceDiagram
    participant E as n8n Execution Engine
    participant G as Google Gemini Node
    participant U as Helper Utils
    participant API as Google Gemini API
    participant EXT as External Storage (URL)

    Note over E, EXT: Image/Video Generation & Processing Flow

    E->>G: execute()
    
    alt Image Generation / Editing
        G->>API: POST /v1beta/models/...:generateContent
        API-->>G: Returns base64 data + mimeType
    else Video Generation (Asynchronous)
        G->>API: POST /v1beta/models/...:generateVideo
        API-->>G: Returns Operation URI
        loop Poll Status
            G->>API: GET Operation Status
            API-->>G: done: true + video uri
        end
        G->>EXT: Download video from URI
        EXT-->>G: Returns Buffer + mimeType
    else Video Download (Direct)
        G->>EXT: Download video from provided URL
        EXT-->>G: Returns Buffer + mimeType
    end

    Note over G, U: NEW: Extension Resolution Logic
    G->>U: NEW: getFilenameFromMimeType(mimeType, baseName, fallback)
    U->>U: Lookup extension using 'mime-types' library
    
    alt MIME type recognized
        U-->>G: Returns e.g., "image.jpg" or "video.webm"
    else MIME type unknown/missing
        U-->>G: Returns fallback (e.g., "image.png" or "video.mp4")
    end

    G->>G: CHANGED: prepareBinaryData(buffer, fileName, mimeType)
    Note right of G: Previously hardcoded to .png or .mp4
    
    G-->>E: Return NodeExecutionData (Binary + JSON)

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[n8n-assistant]

Got released with n8n@2.18.0