docker编译环境
docker镜像
docker pull abdulachik/ffmpeg.js:latest
docker run -it -p 8090:8090 -v /Users/workspace/Downloads/ffmpeg_wasm:/tmp --privileged=true abdulachik/ffmpeg.js:latest /bin/bash
cd /tmp
打开摄像头
<html>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script>
function encodeVideo(){}
function decodeVideo(){
//获得video摄像头区域
let video = document.getElementById("video");
//播放
video.play();
}
function getMedia() {
let constraints = {
//参数
video: {width: 500, height: 500},
audio: true
};
//获得video摄像头区域
let video = document.getElementById("video");
//返回的Promise对象
let promise = navigator.mediaDevices.getUserMedia(constraints);
//then()异步，调用MediaStream对象作为参数
promise.then(function (MediaStream) {
video.srcObject = MediaStream;
video.play();
//调用编码器
encodeVideo();
decodeVideo();
});
}
</script>
<body onl oad="getMedia()">
<video id="video" width="500px" height="500px" autoplay="autoplay"></video>
<video id="video2" width="500px" height="500px" autoplay="autoplay"></video>
</body>
</html>
自定义编译ffmpeg
前端视频帧提取 ffmpeg + Webassembly-1
前端视频帧提取 ffmpeg + Webassembly-2
docker环境的emcc版本
emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 2.0.30 (f782b50a7f8dded7cd0e2c7ee4fed41ab743f5c0)
clang version 14.0.0 (https://github.com/llvm/llvm-project c4048d8f50aaf2c4c13b8d3e138abc34a22da754)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /emsdk/upstream/bin
解码器编译命令
cd ~/ffmpeg
emconfigure ./configure \
--prefix=/tmp/ffmpeg \
--cc="emcc" \
--cxx="em++" \
--ar="emar" \
--enable-cross-compile \
--target-os=none \
--arch=x86_32 \
--cpu=generic \
--disable-ffplay \
--disable-ffprobe \
--disable-asm \
--disable-doc \
--disable-devices \
--disable-pthreads \
--disable-w32threads \
--disable-network \
--disable-hwaccels \
--disable-parsers \
--disable-bsfs \
--disable-debug \
--disable-protocols \
--disable-indevs \
--disable-outdevs \
--disable-swresample
make
make install
对视频进行解码和提取图像主要用到 ffmpeg 的解封装、解码和图像缩放转换相关的接口，主要依赖以下的库
- libavcodec - 音视频编解码
- libavformat - 音视频解封装
- libavutil - 工具函数
- libswscale - 图像缩放&色彩转换
编译为wasm供js调用
export TOTAL_MEMORY=33554432
export FFMPEG_PATH=/tmp/ffmpeg
//EXPORTED_FUNCTIONS 导出供 js 调用的函数
emcc capture.c ${FFMPEG_PATH}/lib/libavformat.a ${FFMPEG_PATH}/lib/libavcodec.a ${FFMPEG_PATH}/lib/libswscale.a ${FFMPEG_PATH}/lib/libavutil.a \
-O3 \
-I "${FFMPEG_PATH}/include" \
-s WASM=1 \
-s TOTAL_MEMORY=${TOTAL_MEMORY} \
-s EXPORTED_FUNCTIONS='["_main", "_free", "_capture"]' \
-s ASSERTIONS=1 \
-s ALLOW_MEMORY_GROWTH=1 \
-o /capture.js
效果
小结
以上实验表明，js调用ffmpeg库好像不能直接调用ffmpeg-mp4.js,需要在c文件中实现
ImageData *capture(int ms, char *path);
然后在html文件中调用
<script src="web-capture.js"></script>
<script>
let button = document.querySelector('#js_button');
let resultContainer = document.querySelector('#js_result');
let fileInput = document.querySelector('#js_file');
let timeInput = document.querySelector('#js_time');
let infoContainer = document.querySelector('#js_info');
button.addEventListener('click', () => {
let file = fileInput.files[0];
let startTime = Date.now();
window.webCapture.capture(file, timeInput.value * 1000, (dataURL, imageInfo) => {
const { width, height, duration } = imageInfo;
resultContainer.innerHTML = `<img src="${dataURL}" />`
infoContainer.innerHTML = `耗时：${Date.now() - startTime}ms<br>宽度：${width}<br>高度：${height}<br>时长：${duration / 1000000}s`;
})
});
</script>