While building VidSimplify, I ran into a frustrating bottleneck: uploading large video files (sometimes 500MB+) to the server for clipping or watermarking was painfully slow, especially over mobile or unstable networks. Users had to wait for the entire file to upload before any processing could even begin — and if the upload failed near the end, they had to restart from scratch.

Imagine you’re uploading a large 500MB video to your app. Using the classic approach, you send the entire file in a single HTTP POST request. What if your connection drops at 95%? You’ll have to start over — a frustrating and time-consuming experience.

Now imagine a smarter system where your video is split into smaller chunks — say 50 chunks of 10MB each. You upload several chunks in parallel. If one chunk fails, you only resend that small piece, not the entire video. Plus, your server can start processing chunks immediately instead of waiting for the full file. Your upload progress bar updates instantly and accurately. This is the power of chunked and resumable uploads.

⚡ Why Chunked Uploads Can Be Faster

Parallel Uploads: Instead of sending one giant file, you can upload multiple smaller chunks simultaneously — typically 3 to 4 parallel HTTP requests. This better utilizes available bandwidth and reduces overall upload time.
Smaller Requests: Each HTTP request transmits a smaller amount of data, which reduces latency and lowers the chance of a timeout or failure per request.
Resumability: If a chunk upload fails, only that chunk needs to be retried instead of restarting the entire upload. This saves time, bandwidth, and user frustration.
Streaming Merge Option: On the server side, you can begin processing or assembling chunks as soon as the first chunks arrive, instead of waiting for the full file upload. This can speed up workflows like transcoding or video clipping.

⏱️ Real-World Example

Uploading a 500MB video:

Your current method: Sends the entire 500MB file in a single POST request. If the upload fails at 95%, the whole upload must restart from zero.
Chunked approach (e.g., 50 chunks of 10MB each):
Uploads can start processing on the server as soon as early chunks arrive.
If chunk #48 fails, only that chunk is re-uploaded.
Users see instant and accurate progress updates on their uploads.

You’ll see significant performance and user experience improvements especially on:

Files larger than 100MB
Slow or congested networks
Mobile users on cellular data
Flaky or unstable Wi-Fi connections

🛑 When It’s Not (Significantly) Faster

If:

You’re uploading very small files (under ~50MB),
Uploads happen over LAN or very fast, stable internet,
Network conditions are nearly perfect and never drop,

Then the difference between chunked uploads and traditional uploads might be negligible. However, for most real-world scenarios — especially with global users, mobile devices, or variable networks — chunked and resumable uploads offer clear advantages.

Diagram

Best Practices & Implementation Tips

Choose the Right Chunk Size: Too small can cause overhead; too large can reduce parallelism benefits. Typical chunk sizes range from 5MB to 10MB.
Limit Parallel Requests: Usually 3–4 parallel chunks balance network use and server load.
Implement Retry Logic: Automatically retry failed chunks with exponential backoff.
Maintain Upload State: Track uploaded chunks server-side to support resumability.
Secure Your API: Validate chunk integrity and authenticate users.
Use Content-Range or Custom Headers: Help the server identify chunk offsets and assemble them correctly.
Leverage Streaming: Start processing chunks on the backend as soon as they arrive to speed up workflows.

Resources to Learn More

Google Drive’s Resumable Upload Protocol
Tus.io: Open protocol for resumable file uploads
AWS S3 Multipart Upload
MDN: Using Fetch with ReadableStreams
Video Processing Pipelines with FFmpeg

Chunked and resumable uploads aren’t just a nice-to-have — they’re essential for delivering a smooth, reliable experience in real-world video-heavy applications. Whether your users are on unstable mobile networks or uploading huge files, this approach saves time, bandwidth, and frustration — and unlocks faster backend processing pipelines.

Why Chunked & Resumable Uploads Are a Game Changer for Video Processing