How FFmpeg Converts Video to GIF

I still remember when I had completed my React playlist and wanted to build a project.
Most project ideas felt boring — school management systems, counters, todo apps.

I wanted to build something unique.

That’s when I came across a Video to GIF converter using the FFmpeg WASM library.
I was excited, and I actually built it.

Project link: Gifity

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I won’t deep dive into who made FFmpeg, why it was made, or its pros and cons — you can search that on Google.

In this blog, I’ll explain how FFmpeg works internally and how it converts one file type into another.

In simple terms, FFmpeg works in 5 steps.

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1. Demuxing

Demuxing means FFmpeg uses demuxers to split your input file into multiple streams.

A stream is simply a continuous flow of data inside a media file, such as:

• video stream
• audio stream

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2. Decoding

In this step, the input file is converted into raw frames:

• Video → raw pixel frames
• Audio → raw PCM samples

Each video frame is basically an image.
Most editing and processing can only happen on this raw data.

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3. Filtering

Filtering receives raw data from the decoder and sends filtered output to the encoder.

This step can be optional.

Common uses:

• resizing
• deinterlacing (fixing combed images to make them clearer)

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4. Encoding

Here, raw data is converted into compressed packets.

Encoding is usually lossy, meaning quality is reduced to decrease file size.
Some encoders are lossless, but they produce much larger files.

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5. Muxing

This is the final stage.

Muxing repackages all processed streams back into one single output file, keeping everything in sync.

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Example FFmpeg Command

What happens internally:

• Demuxing: input.mkv splits into video + audio streams
• Decoding: video → raw frames, audio → raw PCM samples
• Filtering: video resized to 1280×720
• Encoding: video → H.265 (HEVC), audio → AAC
• Muxing: final MP4 file → output.mp4

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If you’ve read this far, thank you for taking the time to read my blog.

This is my first blog, so there might be mistakes — technical or grammatical.
I’m open to suggestions and corrections.

You can follow me; I’ll be writing more tech blogs.

dattebayo 🌟