Pushing the limits of video encoding with WebCodecs
JSNation 2023
👋 Hey there!
I'm Akash Hamirwasia
Writing code @Razorpay. Love building products on the web, trying out new technologies and contributing to open-source.
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Little back story...
- I was building a video editor on the browser to make interesting product videos.
- Everything was going fine until I started writing code for the export process.
- Got stuck at bunch of places... video formats, audio, encoding, muxing, containers, etc.
- Finally figured it out! 🙌
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Drawing a video on the web
- Video is a set of image frames changing at a constant rate.
- Each frame can be rendered in a variety of ways:
- CSS Animation
- Modifying DOM directly with JavaScript
- SVGs
- HTML5 Canvas
- The frames rendered on screen can be recorded and saved as a video file.
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Record something on screen using JavaScript?
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Canvas allows video capture!
Through it's captureStream() API, a part of the MediaStream Recording API.
0123
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Sadly, it's not well-suited for this use case
- No constant framerate.
framerate– maximum framerate in which the video is supposed to be captured. - No option to change video file format.
- Low reliablity.
- Ok quality.
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MediaRecording APIs are not designed to be used for precise and high quality video exports
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Can we capture and encode each frame of the canvas ourself?
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images = []Canvas
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images = []Canvas
Frame 1
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images = [📸
Frame 1
Frame 1
]Canvas
Frame 1
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images = [📸
Frame 1
Frame 1
]Canvas
Frame 2
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images = [📸
Frame 1
Frame 1
📸
Frame 2
Frame 2
]Canvas
Frame 2
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images = [📸
Frame 1
Frame 1
📸
Frame 2
Frame 2
...]Canvas
Frame ...
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How to encode an array of images to a video?
images = [📸
Frame 1
Frame 1
📸
Frame 2
Frame 2
...]Canvas
Frame ...
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Whammy.js
- A realtime JavaScript WebM Encoder.
- Appeared on Hacker News 11 years ago!
- Takes snapshots of canvas as images and encodes them to a video file.
github.com/antimatter15/whammy
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Pros & Cons of these JS libraries
✅ High quality output
✅ Constant framerate
✅ Relatively easy
❌ Very slow
❌ Synchronous
❌ No hardware-acceleration
❌ No choice of video formats
❌ No support for adding audio
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Now what?
WebCodecs
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What is WebCodecs?
- Set of APIs that give low-level access to individual frames of a video stream.
- Supports encoding / decoding of each frame in various formats.
- It's asynchronous and hardware accelerated!
- It's more than just video, supports audio too!
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Video encoding process
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Video encoding process
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Video encoding process
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Let's look at the code to encode videos using WebCodecs
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Creating a VideoEncoder
01
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Creating a VideoEncoder
01
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Configuring the VideoEncoder
01234
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How to find the right codec?
- It's not as easy as .webm, .mp4, .avi, etc.
- They are seemingly random strings!
Eg. vp8, avc1.420034, av01.0.12M.10
video codec != video file format
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Video Encoding 101
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Individual frames
Frame 1
Frame 2
Frame 3
Encoding algorithm
Defines how to convert, compress and store frames of the video
Video stream
Frame 1
Frame 2
Frame 3
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Video stream
Frame 1
Frame 2
Frame 3
Muxer
Video container
video.mp4
Video stream
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Video stream
Audio stream
Subtitles
"Muxer"
Combines(multiplexes) multiple encoded streams to a single container
Video container
video.mp4
Video stream
Audio stream
Subtitles
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What's a codec again?
- Encoding algorithm to convert, compress the individual frames of the video.
- A codec and container must be compatible with each other.
| container | codec | example |
|---|---|---|
| WebM | VP8, AV1 | vp8 |
| MP4 | AVC, AV1 | avc1.420034, av01.0.12M.10 |
- Every browser supports different set of codecs.
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Back to code
0
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Back to code
012
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Back to code
012
download
videoBuffer?akashhamirwasia.comJSNation 2023
Recall the video encoding process
Individual frames
Frame 1
Frame 2
Frame 3
codec
Video stream
Muxer
Video container
video.mp4
Handled by WebCodecs
How do we do this?
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Using ffmpeg.wasm as a muxer
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Using ffmpeg.wasm as a muxer
akashhamirwasia.comJSConf India 2023
Using ffmpeg.wasm as a muxer
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Using ffmpeg.wasm as a muxer
akashhamirwasia.comJSNation 2023
And that's how you encode a video in the browser!
✅ High quality output
✅ Constant framerate
✅ Fast
✅ Asynchronous
✅ Hardware accelerated
✅ Use any video format
✅ Support for adding audio
❌ Relatively hard
✅ Now easy! 🙌
akashhamirwasia.comJSNation 2023
Speaking of browser support...
WebCodecs
WebAssembly
Supported in all browsers 🎉
Remember I was building a tool to make product videos?
Make catchy product videos in just few minutes
Thank you! 💛
Let's connect
Pushing the limits of video encoding with WebCodecs JSNation 2023