aspeed_codec

A javascript decoder which supports aspeed jpeg. The pure javascript(lib/decoder_js.js) and webassembly(lib/decoder_wasm.*) implemenattions are both included. webassembly one will be used if possbile.

Updates

1.0.1 - 2022-03-24

• Fix wasm decoder crash if complex video screen

1.0.0 - 2021-12-03

• Initial release

Steps

Compile your webassembly module

Although the webassembly module is ready, you can also modify and update by yourself.

Make sure your emsdk environment is ready first.

  $ emcc src/decoder.c -o lib/decoder_wasm.js -s ALLOW_MEMORY_GROWTH=1 -s MODULARIZE=1 -s EXPORT_ES6=1 -s EXPORTED_FUNCTIONS="['_malloc', '_free']" -O3

Required Emscripten flags

The table below explains Emscripten-specific build flags required to build this sample:

Flag	Description
-s ALLOW_MEMORY_GROWTH=1	Allows the total amount of memory used to change depending on the demands of the application.
-s EXPORT_ES6=1	Flag will include the necessary export object expected by the import statement.
-s MODULARIZE=1	Flag will wrap the generated JavaScript code’s Module object in a function. EXPORT_ES6 requires MODULARIZE to be set.
-s EXPORTED_FUNCTIONS="['_malloc', '_free']"	Export function, _malloc/_free, to get memory for wasm module usage.

Example Usage

import {decode} from "./lib/decoder.js";

let outbuf = decode(
      header: {
            frame: sequence_number,
            mode420: mode,
            selector: sel,
            advance_selector: adv_sel,
            width: width,
            height: height,
      },
      buffer: data
);

• frame: sequence number of the aspeed jpeg frame, which should continuous increase.
• mode420: 1 for 420, and 0 for 444
• selector: [0~11], the quality of the compressed data which should be the same with the one that video engine used.
• advance_selector: [0~11], the quality of pass-2 compressed data which should be the same with the one that video engine used.
• width: width of the aspeed jpeg
• height: height of the aspeed jpeg
• buffer: the data of the aspeed video engine, which includes aspeed jpeg header and aspeed jpeg data.

Data format

Please refer to Video stream data format – ASPEED mode compression of SDK User Guide of aspeed sdk.