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The LMS Backend handles two types of media uploads: course thumbnails (images) and lecture videos. Both follow the same pipeline — Multer writes the incoming file to a temporary directory on disk, the controller then reads that file path and streams it to Cloudinary, and the returned Cloudinary URL is persisted on the database document. Cloudinary URLs are what you receive back in API responses.

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Upload pipeline

1

Multipart request arrives

Your client sends a multipart/form-data request. Multer is applied as route-level middleware using upload.single(fieldName), where fieldName is either "thumbnail" or "video" depending on the endpoint.
2

Multer writes to disk

The Multer instance is configured with dest: "upload", which writes the uploaded file to a local upload/ directory as a temporary file. The file’s path is available on req.file.path.
utils/multer.js
import multer from "multer";

const upload = multer({ dest: "upload" });

export default upload;
3

Controller uploads to Cloudinary

The controller calls uploadMedia(req.file.path). Cloudinary’s SDK reads the temp file, uploads it with resource_type: "auto" (which automatically detects images and videos), and returns an upload response object.
utils/cloudinary.js
export const uploadMedia = async (file) => {
    try {
        const uploadResponse = await cloudinary.uploader.upload(file, {
            resource_type: "auto"
        });
        return uploadResponse;
    } catch (error) {
        console.log("Error in uploading media to cloudinary.");
        console.log(error);
    }
}
4

Cloudinary URL saved to database

The controller extracts uploadResponse.secure_url and saves it on the relevant document field (e.g. course.thumbnail or lecture.videoUrl). That URL is returned in the API response.

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Supported file types and field names

Cloudinary’s resource_type: "auto" means the SDK infers the type from the file content rather than relying on the MIME type or extension. In practice:
EndpointField nameExpected content
POST /api/v1/coursesthumbnailImage (JPEG, PNG, WebP, etc.)
PATCH /api/v1/courses/:courseIdthumbnailImage (JPEG, PNG, WebP, etc.)
POST /api/v1/courses/:courseId/lecturesvideoVideo (MP4, MOV, WebM, etc.)
PATCH /api/v1/user/profileavatarImage (JPEG, PNG, WebP, etc.)
Multer does not enforce a file size limit or MIME type filter in the current configuration. Cloudinary’s own upload limits apply. Cloudinary free-tier accounts have a 10 MB image limit and a 100 MB video limit per upload.

​
Uploading a course thumbnail

Creating a course requires isAuthenticated middleware and a multipart/form-data body with a thumbnail file field alongside the course text fields: 
curl -b cookies.txt -X POST https://api.example.com/api/v1/courses \
  -F "title=Introduction to Node.js" \
  -F "description=Learn Node.js from the ground up" \
  -F "category=Backend Development" \
  -F "level=Beginner" \
  -F "price=29.99" \
  -F "thumbnail=@/path/to/thumbnail.jpg"
The response includes the Cloudinary URL on the thumbnail field: 
{
  "success": true,
  "message": "Course created successfully",
  "course": {
    "_id": "64f3a...",
    "title": "Introduction to Node.js",
    "thumbnail": "https://res.cloudinary.com/your-cloud/image/upload/v1.../abc123.jpg"
  }
}

​
Adding a lecture with a video

Adding a lecture to an existing course uses upload.single("video"). Send the video file under the video field: 
curl -b cookies.txt \
  -X POST https://api.example.com/api/v1/courses/64f3a.../lectures \
  -F "title=Setting up your environment" \
  -F "description=Install Node.js, npm, and your first Express app" \
  -F "isPreview=false" \
  -F "video=@/path/to/lecture-01.mp4"
The response returns the lecture’s Cloudinary video URL: 
{
  "success": true,
  "message": "Lecture added successfully",
  "lecture": {
    "_id": "64f3b...",
    "title": "Setting up your environment",
    "videoUrl": "https://res.cloudinary.com/your-cloud/video/upload/v1.../lecture01.mp4"
  }
}

​
Updating or replacing media

When you update a course (PATCH /api/v1/courses/:courseId) or a user avatar (PATCH /api/v1/user/profile) with a new file, the controller deletes the old Cloudinary asset before uploading the replacement. Deletion uses the asset’s public_id:
utils/cloudinary.js
export const deleteMediaFromCloudinary = async (publicId) => {
    try {
        await cloudinary.uploader.destroy(publicId)
    } catch (error) {
        console.log("Failed to delete MEDIA from cloudinary");
        console.error(error);
    }
}

export const deleteVideoFromCloudinary = async (publicId) => {
    try {
        await cloudinary.uploader.destroy(publicId, { resource_type: "video" })
    } catch (error) {
        console.log("Failed to delete MEDIA from cloudinary");
        console.error(error);
    }
}
Do not send a Content-Type: application/json header when uploading files. The browser or curl sets the correct multipart/form-data boundary automatically when you use FormData or -F flags. Setting the header manually will break multipart parsing.
The avatar update flow checks whether the existing avatar is the default ("default-avatar.png") before attempting to delete it from Cloudinary. Default avatars are not stored in Cloudinary and do not have a public_id to delete.

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