java音乐播放器后端

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mob64ca13f9a97c 2024-09-07 09:34:00

文章标签 java音乐播放器后端 C 音乐播放器 mpx 音乐播放 文章分类 Java 后端开发

解析音乐播放器实现

简单通俗易懂的方式实现音乐播放功能，阅读代码仅需要C/C++简单基础知识，实现该音乐播放器只使用了microsoft directx sdk几个多媒体控制函数。

#include <dshow.h>
void main(void)
{
    IGraphBuilder *pGraph = NULL;
    IMediaControl *pControl = NULL;
    IMediaEvent   *pEvent = NULL;

    // Initialize the COM library.
    HRESULT hr = CoInitialize(NULL);
    if (FAILED(hr))
    {
        printf("ERROR - Could not initialize COM library");
        return;
    }

    // Create the filter graph manager and query for interfaces.
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, 
                        IID_IGraphBuilder, (void **)&pGraph);
    if (FAILED(hr))
    {
        printf("ERROR - Could not create the Filter Graph Manager.");
        return;
    }

    hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);

    // Build the graph. IMPORTANT: Change this string to a file on your system.
    hr = pGraph->RenderFile(L"C:\\Example.avi", NULL);
    if (SUCCEEDED(hr))
    {
        // Run the graph.
        hr = pControl->Run();
        if (SUCCEEDED(hr))
        {
            // Wait for completion.
            long evCode;
            pEvent->WaitForCompletion(INFINITE, &evCode);

            // Note: Do not use INFINITE in a real application, because it
            // can block indefinitely.
        }
    }
    pControl->Release();
    pEvent->Release();
    pGraph->Release();
    CoUninitialize();
}

基于该例子添加各种控制实现音乐播放器功能

mpx代码解析

mpx工程代码解析

包含mpx.h头文件和mpx.c实现文件

该工程只生成控制音乐播放器用到的静态库mpx.lib

mpx.h头文件源码

/*****************************************************************************
* author menghun3@gmail.com
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation.
* 
* source code address https://github.com/menghun3/mpx
******************************************************************************/
#ifndef MPX_H
#define MPX_H

void mpxInit();
void mpxDestroy();
void mpxPlayFile(void *path);
void mpxPlay();
void mpxPause();
void mpxStop();
int mpxGetCurrentPosition(long long *curpos);
int mpxGetPositions(long long *curpos, long long *stoppos);
int mpxGetStopPosition(long long *stoppos);
int mpxGetVolume(long *plVolume);
int mpxPutVolume(long lVolume);
int mpxGetGuidFormat(GUID *pFormat);
int mpxGetRate(double *dRate);

#endif // MPX_H

使用者只需要调用mpxPlayFile()函数将歌曲文件路径传入即可播放文件，然后使用mpxPause()、mpxStop()、mpxPlay()控制歌曲的暂停、停止、播放。

mpx.c实现文件代码分段解析

完整代码见https://github.com/menghun3/mpx/blob/master/mpx/mpx.c

全局变量

IGraphBuilder *pGraph = NULL;
IMediaControl *pControl = NULL;
IMediaEvent *pEvent = NULL;
IMediaSeeking *pSeek = NULL;
IBasicAudio *pBA = NULL;

HANDLE h = NULL;
int threadid = 0;
HANDLE checkh = NULL;
int chechid = 0;

mpxPlayFile函数

// 播放文件
void mpxPlayFile(void *path)
{
	if (h)
	{
		PostThreadMessage(threadid, PT_QUIT, (WPARAM)0, (LPARAM)0);
		WaitForSingleObject(h, INFINITE);
	}

	h = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)PlayThread, path, 0, (LPDWORD)&threadid);
	if (NULL == h)
	{
		printf("create thread error\n");
		return;
	}
}

该函数创建一个线程控制播放，主要功能在线程PlayThread()函数里面，threadid为全局变量用于结束该线程。

PlayThread函数

void PlayThread(void *param)
{
	WCHAR *songpath = (WCHAR *)param;
	PT_CTROL ptstatus  = PT_LAST;
	InitPlay();
	mpPlay1(songpath);
	ptstatus = PT_PLAY;
	do 
	{
		MSG msg;
		while(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
		{
			switch (msg.message)
			{
			case PT_LOADING:
				{
					WCHAR *path = (WCHAR*)msg.lParam;
					ptstatus = PT_PLAY;
					mpPlay1(path);
				}
				break;
			case PT_PLAY:
				{
					ptstatus = PT_PLAY;
					mpPlay();
				}
				break;
			case PT_PAUSE:
				{
					ptstatus = PT_PAUSE;
					mpPause();
				}
				break;
			case PT_STOP:
				{
					ptstatus = PT_STOP;
					mpStop();
				}
				break;
			case PT_QUIT:
				{
					ptstatus = PT_QUIT;
					mpStop();
					if (checkh)
					{
						CloseHandle(checkh);
						checkh = NULL;
					}
					DestroyPlay();
					return;
				}
				break;
			default:
				{
				}
				break;
			}
		}
	} while (1);
}

该线程函数实现流程为，初始化播放文件需要的环境InitPlay()，然后执行播放文件mpPlay1 ()，再进入消息循环体等待控制信息。

PT_CTROL ptstatus = PT_LAST;用于控制播放状态

typedef enum 
{
	PT_LOADING = 1,
	PT_PLAY,
	PT_PAUSE,
	PT_STOP,
	PT_QUIT,
	PT_LAST
}PT_CTROL;

InitPlay函数

void InitPlay()
{
	HRESULT hr = 0;

	hr = CoInitialize(NULL);
	if (FAILED(hr))
	{
		printf("init com error\n");
		return;
	}

	hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&pGraph);

	if (FAILED(hr))
	{
		printf("create fgm error\n");
		return ;
	}

	hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
	if (FAILED(hr))
	{
		printf("get control error\n");
		return ;
	}
	hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
	if (FAILED(hr))
	{
		printf("get event error\n");
		return;
	}
	hr = pGraph->QueryInterface(IID_IMediaSeeking, (void **)&pSeek);
	if (FAILED(hr))
	{
		printf("get seek error\n");
		return;
	}
}

该函数封装了MSDN例子中初始化环境部分，初始化com，初始化IGraphBuilder对象，及通过IGraphBuilder对象获取以下对象

IMediaControl*pControl=NULL;

IMediaEvent *pEvent = NULL;

IMediaSeeking*pSeek=NULL;

IBasicAudio *pBA = NULL;

mpPlay1函数

void mpPlay1(WCHAR *playSongPath)
{
	HRESULT hr;

	hr = pGraph->RenderFile(playSongPath,NULL);
	if (SUCCEEDED(hr))
	{
		hr = pControl->Run();
		if (FAILED(hr))
		{
			printf("run error\n");
		}
		checkh = CreateThread( NULL, 0, (LPTHREAD_START_ROUTINE)CheckThread, NULL, 0, (LPDWORD)&chechid);
		if (checkh == NULL)
		{
			printf("create chech thread error\n");
		}
	}
	else
	{
		printf("render file error\n");
	}
}

该函数封装MSDN例子中渲染文件及控制运行文件部分代码，此时音乐已经播放，即使没有其他代码音乐一样可以播放完整。

此函数中又创建一个线程，该线程用于检查播放是否到达末尾，每秒检查一次，如果到达末尾则向控制播放的线程发送结束命令，此时控制播放的线程会清理环境。

CheckThread函数

void CheckThread(void *param)
{
	HRESULT hr;
	while (1)
	{
		long long stoppos = 0;
		long long curpos = 0;
		Sleep(1000);
		hr = pSeek->GetPositions(&curpos, &stoppos);
		if (curpos == stoppos)
		{
			PostThreadMessage(threadid, PT_QUIT, NULL, NULL);
			printf("play end\n");
			return;
		}
	}
}

通过IMediaSeeking对象获取当前播放位置及结束位置并作比较，如果相等则说明播放完毕，此时向控制线程发送PT_QUIT命令表示播放结束。

mpPlay、mpStop、mpPause控制函数

这几个函数用户控制音乐播放，实现最简单，被PlayThread线程函数调用控制播放。

void mpPlay()
{
	IMediaControl_Run(pControl);
}

void mpStop()
{
	HRESULT hr = 0;
	long long startpos = 0;
	hr =IMediaSeeking_SetPositions(pSeek, &startpos, AM_SEEKING_AbsolutePositioning, NULL, AM_SEEKING_NoPositioning);
	hr = IMediaControl_Stop(pControl);
}

void mpPause()
{
	HRESULT hr = 0;
	hr = IMediaControl_Pause(pControl);
}

PlayThread调用这几个函数代码如下

while(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
		{
			switch (msg.message)
			{
			case PT_LOADING:
				{
					WCHAR *path = (WCHAR*)msg.lParam;
					ptstatus = PT_PLAY;
					mpPlay1(path);
				}
				break;
			case PT_PLAY:
				{
					ptstatus = PT_PLAY;
					mpPlay();
				}
				break;
			case PT_PAUSE:
				{
					ptstatus = PT_PAUSE;
					mpPause();
				}
				break;
			case PT_STOP:
				{
					ptstatus = PT_STOP;
					mpStop();
				}
				break;
			case PT_QUIT:
				{
					ptstatus = PT_QUIT;
					mpStop();
					if (checkh)
					{
						CloseHandle(checkh);
						checkh = NULL;
					}
					DestroyPlay();
					return;
				}
				break;
			default:
				{
				}
				break;
			}
		}

DestroyPlay函数

void DestroyPlay()
{
	IBasicAudio_Release(pBA);
	pBA = NULL;
	IMediaSeeking_Release(pSeek);
	pSeek = NULL;
	IMediaControl_Release(pControl);
	pControl = NULL;
	IMediaEvent_Release(pEvent);
	pEvent = NULL;
	IGraphBuilder_Release(pGraph);
	pGraph = NULL;
	CoUninitialize();
}

释放对象

mpxPlay、mpxPause、mpxStop对外接口

// 播放
void mpxPlay()
{
	PostThreadMessage(threadid, PT_PLAY, (WPARAM)0, (LPARAM)0);
}

// 暂停
void mpxPause()
{
	PostThreadMessage(threadid, PT_PAUSE, (WPARAM)0, (LPARAM)0);
}

// 停止
void mpxStop()
{
	PostThreadMessage(threadid, PT_STOP, (WPARAM)0, (LPARAM)0);
}

向控制线程发送播放、暂停、停止控制命令。

至此主要功能已经实现，测试程序只要调用

voidmpxPlayFile(void*path);

voidmpxPlay();

voidmpxPause();

voidmpxStop();

这四个函数即可完整控制音乐的播放、暂停、和停止。

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