1、引言
aac 是很常見的音頻格式，壓縮率比mp3 還高，H5 支援從audio 标簽檔案讀取aac 檔案并播放，但不支援從網絡流中直接讀取。這裡借助webassembly 技術，将aac 轉碼成pcm碼流，再借助web audio api 實作aac音頻播放。主要用到的開源庫有faad、pcm-player
2、編譯
進入faad 官網，http://www.linuxfromscratch.org/blfs/view/svn/multimedia/faad2.html，下載下傳faad源碼包并解壓，cd 到工程目錄
cd faad2-2_10_0/
mkdir dist
emconfigure ./configure --prefix=$(pwd)/dist --disable-shared --without-xmms --without-drm --without-mpeg4ip
emmake make
make install
make install 完成後會在dist 目錄生成lib、include 等目錄，裡面存放了faad 頭檔案和庫，複制到路徑備用。
3、faad 使用
一般來說，我不會直接js 調用faad 庫api，而是在外面封裝一層，隻暴露一些必要的接口。
NeAACDecOpen
建立一個編碼器并傳回一個NeAACDecHandle類型句柄
NeAACDecHandle NeAACDecOpen(void)
NeAACDecClose(NeAACDecHandle );
NeAACDecInit2
初始化函數，小于0表示失敗
NEAACDECAPI char NeAACDecInit2(NeAACDecHandle hDecoder,
unsigned char *pBuffer,
unsigned long SizeOfDecoderSpecificInfo,
unsigned long *samplerate,
unsigned char *channels);
參數
hDecoder
NeAACDecOpen 建立的句柄
pBuffer
指向緩存空間，用于儲存轉換後的pcm 資料
SizeOfDecoderSpecificInfo
輸入aac 音頻的大小
sampleRate
音頻采樣率
channels
音頻通道數
NeAACDecDecode
void* NeAACDecDecode(NeAACDecHandle hpDecoder,
NeAACDecFrameInfo *hInfo,
unsigned char *buffer,
unsigned long buffer_size)
hpDecoder
NeAACDecOpen建立的句柄
NeAACDecFrameInfo
NeAACDecFrameInfo 指針
buffer
指向輸入AAC音頻的緩存區
buffer_size
輸入AAC音頻大小
NeAACDecClose
void NeAACDecClose(NeAACDecHandle hpDecoder)
C端完整代碼
#include <memory.h>
#include <stdlib.h>
#include "faad.h"
#include <stdbool.h>
#include <string.h>
#include <emscripten.h>
#include <stdio.h>
#include <sys/time.h>
#include <sys/timeb.h>
#include <unistd.h>
bool hasInit = false;
NeAACDecHandle decoder = 0;
NeAACDecFrameInfo frame_info;
void PrintArry(unsigned char *buffer, unsigned int size)
{
int i;
char data[1024*1024];
for(i = 0;i < size;i++)
{
data[i] = buffer[i];
}
data[i + 1] = '\0';
}
int init_decoder(unsigned char* inBuffer, size_t size)
{
unsigned char channels;
unsigned long sampleRate;
memset(&frame_info, 0, sizeof(frame_info));
decoder = NeAACDecOpen();
NeAACDecInit(decoder, inBuffer, size, &sampleRate, &channels);
//printf("init_decoder初始化完畢\n");
hasInit = true;
return 0;
}
int feedData(unsigned char* out_data, unsigned char* buffer, unsigned int size)
{
int ret = 0;
if (!hasInit)
{
init_decoder(buffer, size);
}
unsigned char *out_buffer = (unsigned char*)NeAACDecDecode(decoder, &frame_info, buffer, size);
//printf("frame_info.error %d\n",frame_info.error);
if (frame_info.error > 0)
{
return frame_info.error;
}
else if(out_buffer && frame_info.samples > 0)//解碼成功
{
ret = frame_info.samples * frame_info.channels;
for(int i = 0;i < ret;i++)
{
out_data[i] = out_buffer[i];
}
}
return ret;
}
void destroyDecoder()
{
hasInit = false;
NeAACDecClose(decoder);
}
4、html 調用
再次進行編譯，将C編譯成 最終目标wasm
export TOTAL_MEMORY=10485760
rm *.js *.wasm
export EXPORTED_FUNCTIONS="[ \
'_malloc' \
,'_free' \
,'_destroyDecoder' \
,'_feedData' \
]"
export LIBRARY_FUNCTIONS="[\
'malloc', \
'free' \
]"
#
emcc aac.c \
-O3 \
-s WASM=1 \
-I /usr/local -lfaad -lm -L ./lib \
-s TOTAL_MEMORY=${TOTAL_MEMORY} \
-s DEFAULT_LIBRARY_FUNCS_TO_INCLUDE="${LIBRARY_FUNCTIONS}" \
-s EXPORTED_FUNCTIONS="${EXPORTED_FUNCTIONS}" \
-o aac.js
最後html 調用
<html>
<head>
<link rel="shortcut icon" href="#" target="_blank" rel="external nofollow" >
</head>
<script type="text/javascript" src="pcm-player.js"></script>
<script type="text/javascript" src="helper.js"></script>
<script src="https://cdn.bootcss.com/vConsole/3.2.0/vconsole.min.js"></script>
<body>
請點選一下螢幕，才能播放聲音
</body>
<script>
var decodeCount = 1;
var isFinish = false;
var socketURL = "ws://192.168.11.66:9101";
socketURL = "ws://127.0.0.1:8080";
let vConsole = new VConsole();
var player = new PCMPlayer({
encoding: '16bitInt',
channels: 2,
sampleRate: 44100,
flushingTime: 22,
debug:false
});
FaadModule = {};
FaadModule.onRuntimeInitialized = function()
{
console.log("Wasm 加載成功!")
isFinish = true;
}
function closeDecoder()//關閉解碼器
{
FaadModule._destroyDecoder();
}
function decodeAAC(data)
{
var retPtr = FaadModule._malloc(4 * 5 * 1024);//接收的資料
var inputPtr = FaadModule._malloc(4 * data.length);//輸入資料
for( i =0;i < data.length;i++)
{
FaadModule.HEAPU8[(inputPtr)+i] = data[i];//轉換為堆資料
}
var pcmLen = FaadModule._feedData(retPtr, inputPtr, data.length);
if(pcmLen >= 0)
{
//console.log("%d幀 aac 解碼成功, %d", decodeCount, pcmLen);
var pcmData = new Uint8Array(pcmLen);
for(i = 0;i < pcmLen;i++)
{
pcmData[i] = FaadModule.HEAPU8[(retPtr)+i]
}
player.feed(pcmData);
}
else
{
console.log("%d幀 aac 解碼失敗, %d", decodeCount, pcmLen);
}
decodeCount++;
FaadModule._free(inputPtr);
FaadModule._free(retPtr);
}
var ws = new WebSocket(socketURL);
ws.binaryType = 'arraybuffer';
ws.addEventListener('open', function (event) {
console.log("發送配置幀");
ws.send(ConfigChannel("RK3923C1201900139"));
});
ws.addEventListener('message',function(event)
{
var input = new Uint8Array(event.data);
if(input[0] == 0xff)
{
//console.log("音頻資料");
if(isFinish)
{
var time = new Date().getTime();
decodeAAC(input);
//console.log("音頻解碼耗時:%d ms", new Date().getTime() - time);
}
}
else
{
//console.log("視訊資料");
}
}
);
</script>
<script type="text/javascript" src="aac.js"></script>
</html>
注： chrome 浏覽器可能需要點選以下才有聲音，跟web-audio api有關 有關。
附件：web端播放aac音頻
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