WebAssembly (Wasm) is a binary instruction format suitable for image and video processing due to its near-native execution speed. 1. It supports compiling into intermediate formats in multiple languages, and runs efficiently in the browser; 2. Image and video processing involves a lot of calculations, and Wasm is more efficient than JavaScript; 3. Select language and tool chains when using it, encapsulate functions to receive image data, and JS passes data to Wasm for processing and passes the results back; 4. Video processing requires controlling frame rate, synchronization and memory management, JS grabs frames and passes them to Wasm for processing and then synthesis; 5. Pay attention to data format conversion, memory allocation and release, performance bottleneck positioning, and browser compatibility issues.

H5 WebAssembly is used for image and video processing. To put it bluntly, it allows the web page to run the original desktop-level high-performance image/video processing algorithm. It is not a replacement for JavaScript, but a supplement, allowing you to achieve near-native processing speed in the browser.

What is WebAssembly? Why is it suitable for image and video processing?

WebAssembly (Wasm for short) is not a new language, but a binary instruction format designed to run efficiently in modern browsers. It supports multiple languages (such as C/C, Rust) to compile into intermediate formats and then executes in the browser.

Image and video processing usually involves a lot of calculations, such as convolution, color space conversion, frame rate control, etc. Although JavaScript is flexible, it has limited operational efficiency. WebAssembly's execution speed is close to native code, and it is especially suitable for this type of CPU-intensive tasks.

For example: If you use JS to make a filter, the effect may be stuttered, but if you write it in C, compile it into Wasm and load it into a web page, the same filter will hardly drop frames.

How to process images using WebAssembly in an H5 project?

I won't talk about the complicated compilation process here, I just talk about how you actually use it in the project.

• Choose language and toolchain : If you are familiar with C/C, you can consider compiling with Emscripten; Rust also has wasm-bindgen and wasm-pack support very well.
• Encapsulation function : encapsulates the core function of image processing into an interface that can receive Uint8Array (image data).
• Pass data to Wasm : Use JS to take image data out of canvas or ImageData and pass it to Wasm module for processing.
• Processing the return result : After Wasm has processed the data, write the result back to canvas through JS or generate a new Blob image.

A common practice is: the front-end uses JS to control the process, and Wasm is responsible for the core algorithm, and the two communicate efficiently through memory sharing (such as WebAssembly.Memory).

How to do video processing? What's the difference with images?

Video processing is essentially batch processing of image frames, but there are several key points:

• Frame rate control : You have to control the processing speed well and not allow frames to accumulate.
• Synchronization issues : Audio and video synchronization, processing frames and play frames.
• Memory management : There are many video frames, large data volume, and poor memory management can easily crash.

Working with videos in Wasm is usually done:

• Crawl video frames with JS (for example, get the current frame through canvas).
• Pass the frame data to Wasm to perform filtering, compression, format conversion and other operations.
• Wasm returns the processed frame, then synthesizes it into a video element through JS or generates a new video stream.

A practical scenario: If you add a "real-time beauty" function to the web page, you can use Wasm as the underlying algorithm and JS controls frame acquisition and rendering.

Some easily overlooked but critical details

• Data format conversion : When image data is transferred from JS to Wasm, RGBA format is usually used, but many algorithms are based on YUV, so be careful not to make mistakes in the intermediate conversion.
• Memory allocation and release : Wasm does not have a garbage collection mechanism like JS. Remember to release the memory allocated by itself, otherwise it is easy to leak memory.
• Performance bottleneck positioning : You think Wasm is very fast, but if it is called frequently or if it is copied too much, it will slow down the overall performance.
• Browser Compatibility : All major browsers support Wasm, but on some low-end devices or older systems, the loading and execution speed may not be as fast as expected.

Overall, WebAssembly's role in image and video processing is becoming increasingly important, especially suitable for projects that require high performance but do not want to give up on web platforms. If used well, it can significantly improve the user experience; if used poorly, it may increase the complexity.

Basically that's it.

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