Is hevc.js faster than libde265 compiled to WASM?

libde265 is slightly faster: hevc.js reaches about 83% of libde265's decode speed when both run as WebAssembly. The trade-off is size and license: hevc.js is 236 KB of WASM (vs ~2 MB) and MIT-licensed (vs LGPL-3.0), and it ships a complete MSE streaming pipeline with dash.js and Shaka Player plugins rather than a raw decoder.

Can ffmpeg.wasm be used for real-time HEVC streaming playback?

ffmpeg.wasm is a general audio/video toolbox oriented toward file processing. Its core is tens of megabytes, the multithreaded build requires SharedArrayBuffer and therefore COOP/COEP headers, and it does not provide an MSE intercept pipeline for streaming players. It is a great tool for transcoding files in the browser, not a drop-in playback fallback for dash.js or Shaka.

How is hevc.js different from h265web.js?

h265web.js is a complete standalone player with its own rendering pipeline (canvas/WebGL) and its own custom license (CYL_Free-1.0). hevc.js is not a player: it is an MIT-licensed fallback layer that plugs into the player you already use (dash.js or Shaka Player), feeds a real SourceBuffer with H.264, and stays dormant when the browser decodes HEVC natively.

hevc.js vs libde265.js vs ffmpeg.wasm vs h265web.js — HEVC in the Browser, Compared

          
            
                
                hevc.js
                libde265.js
                ffmpeg.wasm
                h265web.js
              

            
                Built for
                MSE streaming fallback for dash.js / Shaka Player
                Raw HEVC decoding (proof of concept)
                General A/V toolbox — file processing
                Complete standalone player (live FLV/TS/HLS focus)
              

                WASM size
                236 KB
                ~2 MB
                Tens of MB (core)
                Multiple builds (incl. 256/512 MB memory variants)
              

                License
                MIT
                LGPL-3.0
                MIT wrapper — FFmpeg core LGPL/GPL per build
                Custom (CYL_Free-1.0)
              

                COOP/COEP headers
                Not required
                Not required
                Required for the multithreaded build (SharedArrayBuffer)
                Depends on build
              

                Plugs into dash.js / Shaka
                Yes — drop-in plugins
                No
                No
                No — it is its own player
              

                Output path
                Real SourceBuffer fed with H.264 — the player keeps buffer, seek & ABR control
                Canvas
                Files / buffers
                Canvas / WebGL rendering
              

                Native HEVC passthrough
                Yes — SourceBuffer probe, dormant when native decode exists
                —
                —
                Hardware decode via WebCodecs in its own pipeline
              

                CPU-aware quality control
                Yes — caps the host player's ABR when transcoding falls behind
                —
                —
                —
              

                1080p decode (WASM, single-threaded)
                ~61 fps — 83% of libde265's speed at 1/8th the size
                Baseline (faster, larger)
                Depends on threads/build
                Not published here — see their benchmarks
              

                Validation
                Pixel-perfect vs ffmpeg on 128 bitstreams
                Mature libde265 core, early JS port
                FFmpeg itself
                Production usage at large platforms
              

          
        

	hevc.js	libde265.js	ffmpeg.wasm	h265web.js
Built for	MSE streaming fallback for dash.js / Shaka Player	Raw HEVC decoding (proof of concept)	General A/V toolbox — file processing	Complete standalone player (live FLV/TS/HLS focus)
WASM size	236 KB	~2 MB	Tens of MB (core)	Multiple builds (incl. 256/512 MB memory variants)
License	MIT	LGPL-3.0	MIT wrapper — FFmpeg core LGPL/GPL per build	Custom (CYL_Free-1.0)
COOP/COEP headers	Not required	Not required	Required for the multithreaded build (SharedArrayBuffer)	Depends on build
Plugs into dash.js / Shaka	Yes — drop-in plugins	No	No	No — it is its own player
Output path	Real SourceBuffer fed with H.264 — the player keeps buffer, seek & ABR control	Canvas	Files / buffers	Canvas / WebGL rendering
Native HEVC passthrough	Yes — SourceBuffer probe, dormant when native decode exists	—	—	Hardware decode via WebCodecs in its own pipeline
CPU-aware quality control	Yes — caps the host player's ABR when transcoding falls behind	—	—	—
1080p decode (WASM, single-threaded)	~61 fps — 83% of libde265's speed at 1/8th the size	Baseline (faster, larger)	Depends on threads/build	Not published here — see their benchmarks
Validation	Pixel-perfect vs ffmpeg on 128 bitstreams	Mature libde265 core, early JS port	FFmpeg itself	Production usage at large platforms

Sizes, licenses and capabilities as published by each project (August 2026). Corrections welcome — open an issue.

Which one should you use?

Pick hevc.js if…

You already ship dash.js or Shaka Player and need HEVC streams to play on clients without native HEVC decode — Chrome on Windows without an HEVC-capable GPU, Edge/Firefox without the Microsoft codec extension, Linux fleets. One function call, MIT license, no server changes, dormant when native decode exists.

Pick ffmpeg.wasm if…

You need general media processing in the browser — converting files, extracting frames, transmuxing across dozens of codecs and containers. It's a toolbox, not a playback fallback: no MSE pipeline, and the fast multithreaded build needs COOP/COEP headers.

Pick h265web.js if…

You want a complete, battle-tested standalone player — especially for live surveillance-style workflows (HttpFLV, TS, WebSocket) — and its custom license works for your product. You adopt its player UI and rendering pipeline rather than plugging into your own.

Pick libde265.js if…

You're experimenting with raw HEVC decoding and want the libde265 core in a browser context. It's an early-stage port without a streaming pipeline — for production streaming you'll be building the MSE layer yourself, and the LGPL license may matter for your distribution model.

See hevc.js run

30-second HEVC ABR stream, transcoded to H.264 live in your browser.

Live demo GitHub dash.js plugin docs