The WebCodecs Handbook: Native Video Processing in the Browser

WebCodecs is a browser API enabling hardware-accelerated, frame-level video encoding and decoding without server infrastructure or clunky WASM ports like ffmpeg.js. This comprehensive guide covers video fundamentals (frames, codecs, containers, muxing/demuxing), the core WebCodecs API (VideoFrame, EncodedVideoChunk, VideoEncoder, VideoDecoder), and walks through building a working video converter utility that transcodes between mp4 and webm with resize and flip transformations. The pipeline uses the Streams API for clean state management and memory control. Production concerns covered include codec string selection, bitrate guidance by resolution, GPU vs CPU memory considerations, and the critical need to explicitly call frame.close() to avoid VRAM exhaustion.