Cocos2D-X在WP8上播放mp3
起初竟然不知道用Cocos2D-X在wp8上只能播放wav文件，不能放mp3。要是把mp3全转成wav，太费时费力了。发现不少人也遇到这问题，也有人尝试用Lame做encode/decode代码解决的，比如Lame_WP8，还有mp3之痛 这篇文章都给出了代码。可问题是，这代码莫名其妙之处太多，比如只有一个声道，比如写死的16-bit per sample。最关键是，试了试代码后，发现根本放不了。
开始自己琢磨，还去把Lame原始的例子找来看了看，七拼八凑的做出来了。代码算是self-documented吧，若有不明，欢迎指教。
先找到头文件Cocos2D-X找到CocosDenshion/wp8/MediaStreamer.h，声明两个方法：
...
void Initialize(_In_ const WCHAR* url);
+ void InitializeMp3(_In_ const WCHAR* mp3FilePath);
+ void GetLengthOfId3v2Tag(_In_ const unsigned char * buff, _Outptr_ int * pLength);
void ReadAll(uint8* buffer, uint32 maxBufferSize, uint32* bufferLength);
...
然后编辑CocosDenshion/wp8/MediaStreamer.cpp，include头文件和指明链接库，然后实现这两个方法。
...
#include <lame.h>
#pragma comment(lib, "LibMpgHip")
#pragma comment(lib, "LibMp3Lame")
...
void MediaStreamer::InitializeMp3(__in const WCHAR* mp3FilePath)
{
unsigned int decodedLength = 0;
std::vector<std::unique_ptr<unsigned char[]>> wavBuffer;
std::vector<int> mp3BufferSize;
mp3data_struct mp3Header = {};
struct hip_closer
{
void operator()(hip_t hip) { ::hip_decode_exit(hip); }
};
std::unique_ptr<std::remove_pointer<hip_t>::type, hip_closer> hip(::hip_decode_init());
FILE * pMp3File = nullptr;
struct file_closer
{
void operator()(FILE* file) { ::fclose(file); }
};
ThrowIfFailed(::_wfopen_s(&pMp3File, mp3FilePath, L"rb") == 0);
std::unique_ptr<FILE, file_closer> mp3File(pMp3File);
pMp3File = nullptr;
const int frameBufferSize = 128;
static unsigned char frameBuffer[frameBufferSize];
// If there is ID3 tags start skipping ID3 tags to locate where the MP3 data starts.
size_t readLength = 4;
ThrowIfFailed(::fread_s(frameBuffer, frameBufferSize, 1, readLength, mp3File.get()) == readLength);
if (frameBuffer[0] == 'I' && frameBuffer[1] == 'D' && frameBuffer[2] == '3')
{
readLength = 6;
ThrowIfFailed(::fread_s(&frameBuffer[4], frameBufferSize - 4, 1, readLength, mp3File.get()) == readLength);
GetLengthOfId3v2Tag(&frameBuffer[6], (int *)&readLength);
ThrowIfFailed(::fseek(mp3File.get(), readLength, SEEK_CUR) == 0);
}
else
{
// Reset where we start parsing the MP3 data to the file beginning.
ThrowIfFailed(::fseek(mp3File.get(), 0, SEEK_SET) == 0);
}
int skipSamples = 528 + 1; // There are 529 samples we need to skip. Why 529? Just a MAGIC number from the lame library!
while (::fread_s(frameBuffer, frameBufferSize, 1, frameBufferSize, mp3File.get()) > 0)
{
const int INBUF_SIZE = 1152;
static short pcmL[INBUF_SIZE];
static short pcmR[INBUF_SIZE];
int samples = 0;
// Start looking for MP3 headers
if (!mp3Header.header_parsed)
{
samples = ::hip_decode_headers(hip.get(), frameBuffer, frameBufferSize, pcmL, pcmR, &mp3Header);
continue;
}
samples = ::hip_decode(hip.get(), frameBuffer, frameBufferSize, pcmL, pcmR);
if (samples == -1)
{
break;
}
else if (samples == 0)
{
continue;
}
if (skipSamples > 0
&& skipSamples > samples)
{
skipSamples -= samples;
continue;
}
if (samples > skipSamples)
{
static char decodingBuffer[2 * INBUF_SIZE * 2];
int decodingLength = 0;
int startIndex = skipSamples;
skipSamples = 0;
typedef void(*LeftRightChannelsToBuffer) (const short pcmL, const short pcmR, char * buffer, int & pos);
LeftRightChannelsToBuffer bufferDataMerger = nullptr;
if (mp3Header.stereo == 1)
{
bufferDataMerger = [](const short pcmL, const short pcmR, char * buffer, int & pos)
{
UNREFERENCED_PARAMETER(pcmR);
buffer[pos++] = LO_BYTE(pcmL);
buffer[pos++] = HI_BYTE(pcmL);
};
}
else
{
bufferDataMerger = [](const short pcmL, const short pcmR, char * buffer, int & pos)
{
buffer[pos++] = LO_BYTE(pcmL);
buffer[pos++] = HI_BYTE(pcmL);
buffer[pos++] = LO_BYTE(pcmR);
buffer[pos++] = HI_BYTE(pcmR);
};
}
for (int i = startIndex; i < samples; ++i)
{
bufferDataMerger(pcmL[i], pcmR[i], decodingBuffer, decodingLength);
}
std::unique_ptr<unsigned char[]> decodedBuffer(new (std::nothrow) unsigned char[decodingLength]);
ThrowIfFailed(decodedBuffer);
ThrowIfFailed(::memcpy_s(decodedBuffer.get(), decodingLength, decodingBuffer, decodingLength) == 0);
wavBuffer.emplace_back(decodedBuffer.release());
mp3BufferSize.push_back(decodingLength);
decodedLength += decodingLength;
}
}
ThrowIfFailed(decodedLength > 0);
m_data.resize(decodedLength);
int dataIndex = 0;
for (unsigned int i = 0; i < wavBuffer.size(); ++i)
{
ThrowIfFailed(::memcpy_s((void*)&m_data[dataIndex], mp3BufferSize[i], wavBuffer[i].get(), mp3BufferSize[i]) == 0);
dataIndex += mp3BufferSize[i];
}
m_waveFormat.wFormatTag = WAVE_FORMAT_PCM;
m_waveFormat.nChannels = (WORD)mp3Header.stereo;
m_waveFormat.nSamplesPerSec = mp3Header.samplerate;
m_waveFormat.wBitsPerSample = (mp3Header.samplerate == 96,000) ? 24 : 16; // Sample rate 44,100 or 48,000 is 16 bits/sample but 96,000 is 24 bits/sample.
m_waveFormat.nBlockAlign = m_waveFormat.nChannels * m_waveFormat.wBitsPerSample / 8;
m_waveFormat.nAvgBytesPerSec = m_waveFormat.nSamplesPerSec * m_waveFormat.nBlockAlign;
m_waveFormat.cbSize = 0;
}
用到的inline function for error handling和宏实现在这里：
inline void ThrowIfFailed(bool succeded) {
if (!succeded) {
throw Platform::FailureException::CreateException(E_FAIL, "Unexpected error happened!");
}
}
#define LO_BYTE(x) (x & 0x00ff)
#define HI_BYTE(x) ((x >> 8) & 0x00ff)
然后在原始的MediaStreamer::Initialize(...)方法里，发现是mp3文件时直接调用新方法InitializeMp3(...)。
void MediaStreamer::Initialize(__in const WCHAR* url) {
WCHAR filePath[MAX_PATH] = {0};
...
wcscat_s(filePath, url);
}
+ if (::_wcsicmp(url + urlLength - 4, L".mp3") == 0)
+ {
+ return this->InitializeMp3(filePath);
+ }
Platform::Array<byte>^ data = ReadData(ref new Platform::String(filePath));
...
Okay，把lame_wp8引入项目，如果编译链接无误，应该是可以成功播放mp3了。