Uploading large videos from mobile devices is a common requirement in modern apps – social platforms, e-commerce, education, streaming, and professional tools all rely on reliable media uploads. However, achieving a smooth and stable upload experience on mobile networks is far more challenging than it seems.

For any mobile app development company, ensuring seamless video uploads is a critical part of delivering high-quality mobile experiences.

Mobile environments introduce complications such as:

• Flaky or slow networks  
• Switching between Wi-Fi ↔️ mobile data  
• OS suspending or killing background processes  
• Limited memory and CPU 
• Variable file sizes (from MBs to multiple GBs)  

To solve these challenges, one of the most effective techniques is chunked uploading – splitting large video files into smaller segments and uploading them incrementally.

Why Chunked Uploading Is Essential for Mobile Apps

1. Strong Reliability on Unstable Networks

Mobile networks change constantly:

• Users move between cell towers  
• Connections drop inside buildings  
• Network strength fluctuates  
• Uploads may break mid-way  

If you upload a 1 GB file in a single request and it fails at 90%, you must **restart the entire upload**.

With chunking:

• A file is split into smaller parts (e.g., 5–10 MB)  
• Only the failed chunk needs a retry  
• You never restart from zero  
• Upload continues even if the app is temporarily backgrounded (with proper OS support)

2. Pause & Resume Support

Chunking allows:

• Pause the upload at any point
• Resuming only the missing chunks  
• Continuing even after app restarts  
• Uploading only on Wi-Fi if the user prefers  

These capabilities significantly enhance the overall user experience

3. Better User Feedback & Progress Tracking

Chunked uploads allow the app to:

• Monitor the progress of each chunk
• Show detailed progress metrics (e.g., “57/200 chunks uploaded”)
• Calculate accurate ETA  
• Restore and display meaningful upload status even after the app is reopened

This avoids “stuck at 99%” problems.

4. Backend Scalability and Control

On the server side, smaller requests improve:

• Memory usage  
• Response times  
• Error handling  
• Security validations  

The server can:

• Validate each chunk  
• Consume limited resources per request  
• Support parallel chunk uploads  
• Assemble the final video on completion  

5. Supports Very Large Files

Some mobile upload scenarios involve:

• 1–5 GB training videos  
• High-resolution 4K recordings  
• Multi hours long screen recordings  

Chunking ensures these huge uploads are manageable on mobile hardware.

Chunked Upload Architecture (Client + Server)

Mobile App Responsibilities

The mobile application must:

• Read video file from device storage  
• Calculate the number of chunks  
• Send each chunk in a separate request  
• Handle retries for failed chunks  
• Track completed chunks locally  
• Provide the user with upload progress  
• Support pause/resume  

Backend Responsibilities

The backend should:

• Create an upload session and return a unique `uploadId`  
• Receive multiple chunks for that session  
• Validate and save each chunk  
• Keep track of which chunks were uploaded  
• Reassemble chunks once all are received  
• Delete unused/incomplete uploads periodically  

Here’s what a typical API structure looks like:

Endpoint	Purpose
POST /uploads/init	Create an upload session
PUT /uploads/:uploadId/chunks/:index	Upload individual chunk
GET /uploads/:uploadId/status	Check uploaded chunks
POST /uploads/:uploadId/complete	Finalize & assemble

How Chunk Uploading Works – Step-by-Step

1. Initialization Request

The app starts by requesting an upload session:

POST /uploads/init

{

  “fileName”: “video.mp4”,

  “fileSize”: 1200400000,

  “mimeType”: “video/mp4”

}

Backend responds:

{

  “uploadId”: “abc123”,

  “chunkSize”: 5242880,

  “maxRetries”: 3

}

2. Split the Video Into Chunks

The app splits the file:

totalChunks = ceil(fileSize / chunkSize)

for i in range(0, totalChunks):

    start = i * chunkSize

    end = start + chunkSize

    readBytes(start, end)

3. Upload Each Chunk Individually

Each chunk is uploaded with metadata:

PUT /uploads/abc123/chunks/0

Content-Type: application/octet-stream

Headers:

  X-Upload-Id: abc123

  X-Chunk-Index: 0

  X-Total-Chunks: 220

4. Retry Failed Chunks

If a chunk fails:

• Retry it automatically  
• Retry only that chunk  
• Pause upload if retries exceed limits  

Chunking makes failures inexpensive.

5. Complete the Upload

Once all chunks are uploaded:

POST /uploads/abc123/complete

Backend checks chunk completeness and assembles the final file:

{

  “status”: “completed”,

  “fileUrl”: “https://cdn.example.com/videos/xyz789.mp4”,

  “videoId”: “xyz789”

}

6. Resume Support

On app restart, the client can request:

GET /uploads/abc123/status

Backend returns:

{

  “uploadedChunks”: [0,1,2,5,6],

  “missingChunks”: [3,4,7,8,9]

}

The app uploads only missing chunks.

Best Practices for Implementing Chunked Uploads

1. Choose Optimal Chunk Size

Recommended: 5–10 MB per chunk

• Too small → too many requests  
• Too large → heavy retries & memory spikes  

2. Store Upload State Locally

Track:

• Current chunk index  
• UploadId  
• Completed chunk list  
• File path  
• Total chunks  

Use local storage that persists across app restarts.

3. Backend Should Accept Out-of-Order Chunks

This allows:

• Parallel uploads  
• Safe retries  
• Faster completion  

Never force sequential chunk arrival.

4. Secure Every Request

Attach authentication to each chunk request.

5. Clean Up Old Upload Sessions

If an upload is abandoned:

• Remove temporary chunks  
• Free storage  
• Expire the upload session  

6. Support Background Uploading

Depending on your tech stack (native, cross-platform), use OS capabilities such as:

• Background services (Android)
• Background URL sessions (iOS)  

This ensures the upload continues if:

• User locks the screen  
• Switches apps  
• Temporarily leaves the app  

7. Validate Each Chunk

Server can check:

• Chunk size  
• Checksums  
• Correct chunk index  
• Malicious or invalid data  

Conclusion

Chunked uploading is the most reliable method for uploading large videos in mobile applications. It provides:

• High reliability on unstable mobile networks  
• True pause/resume upload functionality  
• Accurate progress updates  
• Backend scalability  
• Ability to support files of any size  

Whether you’re building a social media app, an educational platform, a video-reporting system, or a content-creation tool, chunked uploads ensure your users never suffer frustrating upload failures.