编译WebAssembly版本的FFmpeg（ffmpeg.wasm）：（3）ffmpeg.wasm v0.1 - 将avi转为mp4的编码

#!/bin/bash -x

# verify Emscripten version
emcc -v

# configure FFMpeg with Emscripten
CFLAGS="-s USE_PTHREADS -O3"
LDFLAGS="$CFLAGS -s INITIAL_MEMORY=33554432" # 33554432 bytes = 32 MB
CONFIG_ARGS=(
  --target-os=none        # use none to prevent any os specific configurations
  --arch=x86_32           # use x86_32 to achieve minimal architectural optimization
  --enable-cross-compile  # enable cross compile
  --disable-x86asm        # disable x86 asm
  --disable-inline-asm    # disable inline asm
  --disable-stripping     # disable stripping
  --disable-programs      # disable programs build (incl. ffplay, ffprobe & ffmpeg)
  --disable-doc           # disable doc
  --extra-cflags="$CFLAGS"
  --extra-cxxflags="$CFLAGS"
  --extra-ldflags="$LDFLAGS"
  --nm="llvm-nm -g"
  --ar=emar
  --as=llvm-as
  --ranlib=llvm-ranlib
  --cc=emcc
  --cxx=em++
  --objcc=emcc
  --dep-cc=emcc
)
emconfigure ./configure "${CONFIG_ARGS[@]}"

# build dependencies
emmake make -j4

# build ffmpeg.wasm
mkdir -p wasm/dist
ARGS=(
  -I. -I./fftools
  -Llibavcodec -Llibavdevice -Llibavfilter -Llibavformat -Llibavresample -Llibavutil -Llibpostproc -Llibswscale -Llibswresample
  -Qunused-arguments
  -o wasm/dist/ffmpeg.js fftools/ffmpeg_opt.c fftools/ffmpeg_filter.c fftools/ffmpeg_hw.c fftools/cmdutils.c fftools/ffmpeg.c
  -lavdevice -lavfilter -lavformat -lavcodec -lswresample -lswscale -lavutil -lm
  -O3                                           # Optimize code with performance first
  -s USE_SDL=2                                  # use SDL2
  -s USE_PTHREADS=1                             # enable pthreads support
  -s PROXY_TO_PTHREAD=1                         # detach main() from browser/UI main thread
  -s INVOKE_RUN=0                               # not to run the main() in the beginning
  -s EXPORTED_FUNCTIONS="[_main, _proxy_main]"  # export main and proxy_main funcs
  -s EXTRA_EXPORTED_RUNTIME_METHODS="[FS, cwrap, setValue, writeAsciiToMemory]"   # export preamble funcs
  -s INITIAL_MEMORY=33554432                    # 33554432 bytes = 32 MB
)
emcc "${ARGS[@]}"

$ ffmpeg -hide_banner

Hyper fast Audio and Video encoder
usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...
Use -h to get full help or, even better, run 'man ffmpeg'

const Module = require('./dist/ffmpeg-core.js');

Module.onRuntimeInitialized = () => {
  const ffmpeg = Module.cwrap('proxy_main', 'number', ['number', 'number']);
};

$ node --experimental-wasm-threads --experimental-wasm-bulk-memory ffmpeg.js

const str = "FFmpeg.wasm";
const buf = Module._malloc(str.length + 1); // Allocate a memory with extra byte with value 0 to indicate the end of the string
Module.writeAsciiToMemory(str, buf);

const ptrs = [123, 3455];
const buf = Module._malloc(ptrs.length * Uint32Array.BYTES_PER_ELEMENT);
ptrs.forEach((p, idx) => {
  Module.setValue(buf + (Uint32Array.BYTES_PER_ELEMENT * idx), p, 'i32');
});

const Module = require('./dist/ffmpeg-core');

Module.onRuntimeInitialized = () => {
  const ffmpeg = Module.cwrap('proxy_main', 'number', ['number', 'number']);
  const args = ['ffmpeg', '-hide_banner'];
  const argsPtr = Module._malloc(args.length * Uint32Array.BYTES_PER_ELEMENT);
  args.forEach((s, idx) => {
    const buf = Module._malloc(s.length + 1);
    Module.writeAsciiToMemory(s, buf);
    Module.setValue(argsPtr + (Uint32Array.BYTES_PER_ELEMENT * idx), buf, 'i32');
  })
  ffmpeg(args.length, argsPtr);
};

const fs = require('fs');
const Module = require('./dist/ffmpeg-core');

Module.onRuntimeInitialized = () => {
  const data = Uint8Array.from(fs.readFileSync('./flame.avi'));
  Module.FS.writeFile('flame.avi', data);

  const ffmpeg = Module.cwrap('proxy_main', 'number', ['number', 'number']);
  const args = ['ffmpeg', '-hide_banner'];
  const argsPtr = Module._malloc(args.length * Uint32Array.BYTES_PER_ELEMENT);
  args.forEach((s, idx) => {
    const buf = Module._malloc(s.length + 1);
    Module.writeAsciiToMemory(s, buf);
    Module.setValue(argsPtr + (Uint32Array.BYTES_PER_ELEMENT * idx), buf, 'i32');
  })
  ffmpeg(args.length, argsPtr);
};

const fs = require('fs');
const Module = require('./dist/ffmpeg-core');

Module.onRuntimeInitialized = () => {
  const data = Uint8Array.from(fs.readFileSync('./flame.avi'));
  Module.FS.writeFile('flame.avi', data);

  const ffmpeg = Module.cwrap('proxy_main', 'number', ['number', 'number']);
  const args = ['ffmpeg', '-hide_banner', '-report', '-i', 'flame.avi', 'flame.mp4'];
  const argsPtr = Module._malloc(args.length * Uint32Array.BYTES_PER_ELEMENT);
  args.forEach((s, idx) => {
    const buf = Module._malloc(s.length + 1);
    Module.writeAsciiToMemory(s, buf);
    Module.setValue(argsPtr + (Uint32Array.BYTES_PER_ELEMENT * idx), buf, 'i32');
  });
  ffmpeg(args.length, argsPtr);

  /*
   * The execution of ffmpeg is not synchronized,
   * so we need to parse the log file to check if completed.
   */
  const timer = setInterval(() => {
    const logFileName = Module.FS.readdir('.').find(name => name.endsWith('.log'));
    if (typeof logFileName !== 'undefined') {
      const log = String.fromCharCode.apply(null, Module.FS.readFile(logFileName));
      if (log.includes("frames successfully decoded")) {
        clearInterval(timer);
        const output = Module.FS.readFile('flame.mp4');
        fs.writeFileSync('flame.mp4', output);
      }
    }
  }, 500);

};