?? acm采樣頻率轉換_混亂思維.htm
字號:
href="http://hi.baidu.com/yrworld/profile">個人檔案</A> <SPAN>|</SPAN><A
href="http://hi.baidu.com/yrworld/friend">好友</A> </DIV></DIV>
<DIV class=stage>
<DIV class=stagepad>
<DIV style="WIDTH: 100%">
<TABLE class=modth cellSpacing=0 cellPadding=0 width="100%" border=0>
<TBODY>
<TR>
<TD class=modtl width=7> </TD>
<TD class=modtc noWrap>
<DIV class=modhead><SPAN class=modtit>查看文章</SPAN></DIV></TD>
<TD class=modtc noWrap align=right></TD>
<TD class=modtr width=7> </TD></TR></TBODY></TABLE>
<DIV class=modbox id=m_blog>
<DIV class=tit>ACM采樣頻率轉換</DIV>
<DIV class=date>2008-07-14 11:16</DIV>
<TABLE style="TABLE-LAYOUT: fixed">
<TBODY>
<TR>
<TD>
<DIV class=cnt id=blog_text>ACM采樣頻率轉換
<BR>在音頻的處理中，采樣頻率的轉換是經常碰到的問題，比如輸入44.1k，要求輸出48k，或者相反從48k轉換到44.1k。表面上看來，只是增加或減少采樣點而已。其實不然。如果只是簡單地從時間域上進行采樣點的增減，必然導致原有波形的改變，從而聲音失真，嚴重的時候更是不堪入耳。
<BR><CLK></CLK>正確的方法，應該是對輸入的數據進行FFT變換到頻域，然后再進行轉化。這是一個比較繁瑣的過程。那么，有沒有更簡單一點的方法呢？答案是肯定的。微軟提供了一套ACM的API函數可以幫<NOBR
style="COLOR: #6600ff; BORDER-BOTTOM: #6600ff 1px dotted; BACKGROUND-COLOR: transparent; TEXT-DECORATION: underline">我們</NOBR>的忙。熟悉DirectShow
Filter的朋友更加知道，在SDK中提供的Filter中就有一個叫ACM Wrapper的，其實它就是微軟對ACM
API函數的包裝?？梢哉f，ACM Wrapper Filter是ACM API在DirectShow環境中應用形式。美中不足的是，經過ACM
Wrapper
Filter進行采樣頻率轉化后，由于浮點運算的誤差，有可能會導致數據的丟失。每次轉化的一點點丟失，如果再經過時間上的累加，音頻數據會丟得越來越多。由于微軟的DirectShow是基于Playback模式的一套架構，時間戳上顯示的數據丟失對于人耳根本微不足道。所以僅從播放的角度上來說，這個“問題”是很難被察覺的。如果你要使用經過ACM
Wrapper Filter轉化后的數據跟視頻流合成，那么，你生成的文件很有可能在半個小時或更長的一段時間后出現音視頻的不同步現象。
<BR>解決的辦法有兩種，一種是自己開發一個In-place-transform的Filter。這個Filter緊跟著接到ACM Wrapper
Filter的后面，對進來的每一個Sample檢查時間戳，如果累加的音頻丟失“時間”超過一個采樣點的時間，則馬上補上一個采樣點的數據。另外一種解決方法，就是干脆使用ACM
API函數寫一個自己的ACM Wrapper Filter。這樣，就可以直接在ACM Wrapper內部監視數據的丟失。
<BR>下面我們就來看一下ACM API的使用。請先確認包含了以下頭文件：mmreg.h, mmsytem.h,
msacm.h；以及連接了以下庫文件：msacm32.lib,
winmm.lib。在進行采樣頻率轉換之前，首先要使用acmStreamOpen函數打開一個轉化流，以及對輸入輸出數據類型的設置。示例代碼如下：
<BR>bool CConversionStream::OpenStream(void) <BR>{ <BR>DWORD maxSize = 0;
<BR>MMRESULT mmr = acmMetrics(NULL, ACM_METRIC_MAX_SIZE_FORMAT,
&maxSize); <BR>bool pass = (mmr == MMSYSERR_NOERROR); <BR>if (pass)
<BR>{ <BR>LPWAVEFORMATEX sourceFormat = (LPWAVEFORMATEX) new char
[maxSize]; <BR>LPWAVEFORMATEX destFormat = (LPWAVEFORMATEX) new char
[maxSize]; <BR>memset(sourceFormat, 0, maxSize); <BR>memset(destFormat, 0,
maxSize); <BR>sourceFormat->wFormatTag = WAVE_FORMAT_PCM;
<BR>sourceFormat->nChannels = 2; <BR>sourceFormat->nSamplesPerSec =
44100; <BR>sourceFormat->wBitsPerSample = 16;
<BR>sourceFormat->cbSize = 0; <BR>sourceFormat->nBlockAlign = 4;
<BR>sourceFormat->nAvgBytesPerSec = 44100 * 4;
<BR><BR>destFormat->wFormatTag = WAVE_FORMAT_PCM;
<BR>destFormat->nChannels = 2; <BR>destFormat->nSamplesPerSec =
48000; <BR>destFormat->wBitsPerSample = 16; <BR>destFormat->cbSize =
0; <BR>destFormat->nBlockAlign = 4; <BR>destFormat->nAvgBytesPerSec
= 48000 * 4; <BR><BR>mmr = acmStreamOpen(&mStreamHandler, NULL,
sourceFormat, destFormat, NULL, 0, 0, 0); <BR>pass = (mmr ==
MMSYSERR_NOERROR); <BR>delete[] sourceFormat; <BR>delete[] destFormat;
<BR>} <BR>return pass; <BR>} <BR>/* <BR>實際的數據轉化也很簡單。首先要建立一個ACM
header，并對其進行設置，如果輸入數據的緩沖及數據長度，輸出數據的緩沖及緩沖大小。之后務必調用acmStreamPrepareHeader函數對這個ACM
header進行初始化。然后就調用acmStreamConvert進行數據轉換。最后不要忘記調用acmStreamUnprepareHeader。
<BR>*/ <BR>bool CConversionStream::DoConverting(unsigned char *
inSourceBuffer, long inSourceLength, <BR>unsigned char * outDestBuffer,
long * ioDestLength) <BR>{ <BR>memset(mAcmheader, 0,
sizeof(ACMSTREAMHEADER)); <BR>DWORD suggestedDestSize = 0;
<BR>acmStreamSize(mStreamHandler, inSourceLength, &suggestedDestSize,
ACM_STREAMSIZEF_SOURCE); <BR>ASSERT(suggestedDestSize <=
*ioDestLength); <BR><BR>// Build ACM header on buffer
<BR>mAcmheader->cbStruct = sizeof(ACMSTREAMHEADER);
<BR>mAcmheader->cbSrcLength = inSourceLength; <BR>mAcmheader->pbSrc
= inSourceBuffer; <BR>mAcmheader->cbDstLength = *ioDestLength;
<BR>mAcmheader->pbDst = outDestBuffer; <BR><BR>// Prepare the buffer
for ACM <BR>MMRESULT mmr = acmStreamPrepareHeader(mStreamHandler,
mAcmheader, 0); <BR>bool pass = (mmr == MMSYSERR_NOERROR); <BR>if (pass)
<BR>{ <BR>mmr = acmStreamConvert(mStreamHandler, mAcmheader,
ACM_STREAMCONVERTF_BLOCKALIGN); <BR>pass = (mmr == MMSYSERR_NOERROR);
<BR>} <BR>*ioDestLength = mAcmheader->cbDstLengthUsed;
<BR>ASSERT(mAcmheader->cbSrcLengthUsed == mAcmheader->cbSrcLength);
<BR>// Unprepare ACM header <BR>acmStreamUnprepareHeader(mStreamHandler,
mAcmheader,0); <BR>return pass; <BR>}
<BR><BR>就這么簡單！輕輕松松，實現了音頻的采樣頻率轉換。最后，當所有數據都已經轉換完畢，不要忘了調用acmStreamClose函數關閉轉化流。 </DIV></TD></TR></TBODY></TABLE><BR>
<DIV class=opt><A title=查看該分類中所有文章
href="http://hi.baidu.com/yrworld/blog/category/Directshow">類別：Directshow</A> |
<A title=將此文章添加到百度搜藏 onclick="return addToFavor();"
href="http://cang.baidu.com/do/add" target=_blank>添加到搜藏</A> | 瀏覽(<SPAN
id=result></SPAN>) | <A
href="http://hi.baidu.com/yrworld/blog/item/da041ad1e12309d6562c8495.html#send">評論</A> (0)
<SCRIPT language=javascript>/*<![CDATA[*/var pre = [true,'設置音頻sourcefilterk 中的WAVEFORMATEX結構', '設置音頻sourcefilterk 中的WAVE...','/yrworld/blog/item/24c5f5dd099364ea77c6381d.html'];var post = [true,'DirectShow系統初級指南','DirectShow系統初級指南', '/yrworld/blog/item/2ce011e987253639b90e2d7f.html'];if(pre[0] || post[0]){ document.write('<div style="height:5px;line-height:5px;"> </div><div id="in_nav">'); if(pre[0]){ document.write('上一篇：<a href="' + pre[3] + '" title="' + pre[1] + '">' + pre[2] + '</a> '); } if(post[0]){ document.write('下一篇：<a href="' + post[3] + '" title="' + post[1] + '">' + post[2] + '</a>'); } document.write('</div>');}/*]]>*/</SCRIPT>
</DIV>
<DIV class=line></DIV>
<STYLE type=text/css>#in_related_doc A {
TEXT-DECORATION: none
}
</STYLE>
<DIV id=in_related_tmp></DIV>
<SCRIPT language=javascript type=text/javascript>/*<![CDATA[*/function HI_MOD_IN_RELATED_DOC_CALLBACK(arg){ if(arg.length <= 1) return false; var hasMore = arg[0]; var D=function(A,B){A[A.length]=B;} if(arg.length % 2 == 0) D(arg, ["","","",""]); var html = ['<div id="in_related_doc"><div class="tit">相關文章：</div>']; D(html, '<table cellpadding="0" cellspacing="3" border="0">'); for(var i = 1, j = arg.length; i < j; i += 2){ D(html, '<tr>'); D(html, '<td width="15px"><a style="font-size:25px" >•</a></td><td><a href="http://hi.baidu.com/' + arg[i][3] + '/blog/item/' + arg[i][2] + '.html" target="_blank" title="' + arg[i][0] + '">' + arg[i][1] + '</a>'); D(html, new Array(10).join('\u3000')); D(html, '</td>'); if(arg[i + 1][0] != "") D(html, '<td width="15px"><a style="font-size:25px" >•</a></td><td><a href="http://hi.baidu.com/' + arg[i + 1][3] + '/blog/item/' + arg[i + 1][2] + '.html" target="_blank" title="' + arg[i + 1][0] + '">' + arg[i + 1][1] + '</a></td>'); else D(html, '<td> </td><td> </td>'); D(html, '</tr>'); } if(hasMore) D(html, '<tr><td colspan="4"><a target="_blank" href="/sys/search?pageno=1&type=7&sort=1&word=ACM%B2%C9%D1%F9%C6%B5%C2%CA%D7%AA%BB%BB&item=da041ad1e12309d6562c8495">更多>></a></td></tr>'); D(html, '</table></div><div class="line"> </div>'); var div = document.getElementById('in_related_tmp'); if(div){ div.innerHTML = html.join(''); while(div.firstChild){ div.parentNode.insertBefore(div.firstChild, div); } div.parentNode.removeChild(div); } window.setTimeout("tracker_init('in_related_doc')",100);}if(RelatedDocData == -1){ // not supported xhr var script = document.createElement('script'); script.type = 'text/javascript'; script.src = '/sys/search?type=8&word=ACM%B2%C9%D1%F9%C6%B5%C2%CA%D7%AA%BB%BB&item=da041ad1e12309d6562c8495&t=' + new Date().getTime(); document.getElementsByTagName('HEAD')[0].appendChild(script);}else if(RelatedDocData == null){ GetAndEval = true;}else{ eval(RelatedDocData);}/*]]>*/</SCRIPT>
<DIV id=in_reader>
<DIV class=tit>最近讀者：</DIV>
<SCRIPT> var g_spAnnony=true;var g_read=[ ["acfly","980f5f41435f666c795f2e05","_AC_fly_"],{}];g_read.length=g_read.length-1;var _rh1="";var _rh2="";function wrreader(){ _rh1 += '<table width="100%" ><tr>'; _rh2+='<tr>'; if(g_spAnnony){ _rh1+='<td align="center" width="10%" ><img border="0" width="55" height="55" src="http://img.baidu.com/hi/img/portraitn.jpg"></td>'; _rh2+='<td> </td>'; if(g_read.length>0){ _rh1+='<td align="left" width="12%">'; }else{ _rh1+='<td align="left" width="100%">'; } _rh1+='<a href="http://passport.baidu.com/?login&tpl=sp&tpl_reg=sp&u='+myref+'" target="_self">登錄</a>后，您就出現在這里。</td>'; _rh2+='<td> </td>' } if(g_read.length==0){ if(!g_spAnnony){ _rh1+='<td align=left width="100%">最近還沒有登錄用戶看過這篇文章……</td>'; _rh2+='<td> </td>'; } }else{ for(i=0,len=g_read.length;i<len;i++){ _rh1+='<td align="center" valign="bottom" width="10%" class="user"><a href="/'+g_read[i][0]+'" target="_blank"><img border="0" src="http://himg.baidu.com/sys/portraitn/item/'+g_read[i][1]+'.jpg"></a></td>'; _rh2+='<td align="center" valign="top" class="user"><a href="/'+g_read[i][0]+'" target="_blank">'+g_read[i][2]+'</a></td>'; } } _rh1+='<td width="100%"></td></tr>'; _rh2+='<td></td></tr></table>'; document.write(_rh1+_rh2);}wrreader();</SCRIPT>
</DIV>
<DIV class=line></DIV>
<SCRIPT language=JavaScript>allkey=allkey+"fa45d9eab43e26d3d439c985_da041ad1e12309d6562c8495_";</SCRIPT>
<DIV id=in_comment><A name=comment></A>
<DIV class=tit>網友評論：</DIV>
<SCRIPT>function writecmt(type,id,cmtname,cmturl,portraitId){ var html1=""; if(type==1){ html1="<a href='"+cmturl+"' target='_blank' title='"+cmturl+"'><img border='0' src='http://himg.baidu.com/sys/portraitn/item/"+portraitId+".jpg'><br>"+cmtname+"</a>"; }else{ if(cmtname=="" || cmtname=="匿名網友"){ if(cmturl==""){ html1="<a>匿名網友</a>"; }else{ html1="<a href='"+cmturl+"' target='_blank' title='"+cmturl+"'>"+cmtname+"</a>"; } }else{ if(cmturl==""){ html1="<div class='f14' style='display:inline'>網友:<a>"+cmtname+"</a></div>"; }else{ html1="<div class='f14' style='display:inline'>網友:<a href='"+cmturl+"' target='_blank' title='"+cmturl+"'>"+cmtname+"</a></div>"; } } } document.write(html1);}</SCRIPT>
<DIV id=page></DIV></DIV>
<DIV id=in_send><A name=send></A>
<FORM id=popFormSubmit name=form1 onsubmit="return checkcmtform()"
action=/yrworld/commit method=post><INPUT type=hidden value=8 name=ct> <INPUT
type=hidden value=1 name=cm> <INPUT type=hidden value=da041ad1e12309d6562c8495
name=spBlogID> <INPUT id=spRefURL type=hidden name=spRefURL>
<SCRIPT> document.getElementById("spRefURL").value = window.location.href;</SCRIPT>
<DIV class=tit>發表評論：</DIV>
<TABLE cellSpacing=5 cellPadding=0 width=620 border=0>
<TBODY>
<TR>
<TD class=f14>姓 名：</TD>
<TD><INPUT id=spBlogCmtor style="WIDTH: 220px" onfocus=hidErr(1);
tabIndex=1 maxLength=49 onchange="checkname('spBlogCmtor')"
name=spBlogCmtor>
<SCRIPT>document.write(" <a href='http://passport.baidu.com/?reg&tpl=sp&return_method=get&skip_ok=1&u=http://hi.baidu.com/sys/reg/' target='_blank'>注冊</a>");document.write(' | <a href="http://passport.baidu.com/?login&tpl=sp&tpl_reg=sp&u='+myref+'">登錄</a>');</SCRIPT>
<DIV id=nmerror style="DISPLAY: none">*姓名最長為50字節</DIV></TD></TR>
<TR id=1_err style="DISPLAY: none">
<TD> </TD>
<TD>
<DIV class=error id=1_err_con></DIV></TD></TR>
<TR>
<TD class=f14>網址或郵箱：</TD>
<TD><INPUT id=spBlogCmtURL style="WIDTH: 360px" onfocus=hidErr(2);
tabIndex=2 maxLength=128 onchange="checkeandu('spBlogCmtURL')"
name=spBlogCmtURL> (選填)</TD>
<SCRIPT>G("spBlogCmtor").value="";G("spBlogCmtURL").value="";</SCRIPT>
</TR>
<TR id=2_err style="DISPLAY: none">
<TD> </TD>
<TD>
<DIV class=error id=2_err_con></DIV></TD></TR>
<TR>
<TD class=f14 vAlign=top>內 容：</TD>
<TD><TEXTAREA id=spBlogCmtText style="WIDTH: 520px; HEIGHT: 155px" onfocus=hidErr(3); tabIndex=3 name=spBlogCmtText></TEXTAREA>
<SCRIPT>G("spBlogCmtor").value=G("spBlogCmtor").defaultValue;G("spBlogCmtText").value="";</SCRIPT>
</TD></TR>
<TR id=3_err style="DISPLAY: none">
<TD> </TD>
<TD>
<DIV class=error id=3_err_con></DIV></TD></TR>
<TR id=vercode>
<TD class=f14 vAlign=top>驗證碼：</TD>
<TD vAlign=top><INPUT type=hidden
value=3035737061636531393034393330373538303030303030303030303030303031323235363832353036A0200428076174F5DDF9A192D6A01665
name=spVcode> <INPUT id=spVerifyKey onfocus=f_focus() tabIndex=4
maxLength=4 size=6 name=spVerifyKey autocomplete="off"><BR>
<SCRIPT type=text/javascript>/*<![CDATA[*/var imgsrc="http://hiup.baidu.com/cgi-bin/genimg?3035737061636531393034393330373538303030303030303030303030303031323235363832353036A0200428076174F5DDF9A192D6A01665";function f_focus(){ if(G('yanzheng').style.display=="none" ){ G('verifypic').src=imgsrc; G('yanzheng').style.display="block"; }}function newverifypic(){ G("verifypic").src = imgsrc +"&t="+ Math.random(); return false;}/*]]>*/</SCRIPT>
<DIV id=yanzheng style="DISPLAY: none"><IMG id=verifypic height=40
width=120><WBR><A title=看不清左邊的字符 onfocus=this.blur();
onclick="return newverifypic();"
href="http://hi.baidu.com/yrworld/blog/item/da041ad1e12309d6562c8495.html#">看不清?</A>
</DIV></TD></TR>
<TR>
<TD class=f14 vAlign=top> </TD>
<TD class=f14 vAlign=top><INPUT id=btn_ok tabIndex=5 type=submit value=發表評論 name=btn_ok></TD></TR></TBODY></TABLE></FORM></DIV><BR></DIV>
<TABLE height=8 cellSpacing=0 cellPadding=0 width="100%" border=0>
<TBODY>
<TR>
<TD class=modbl width=7> </TD>
<TD class=modbc> </TD>
<TD class=modbr width=7> </TD></TR></TBODY></TABLE></DIV></DIV></DIV></DIV>
<SCRIPT language=javascript><!--var hstr="/yrworld/brwstat?key1=1";document.write("<script src='"+hstr+"&key2="+allkey+"'><\/script>");//--></SCRIPT>
<BR>
<CENTER>
<DIV id=ft>©2008 Baidu</DIV></CENTER>
<SCRIPT>if(document.getElementById("m_blog")){ var imgarray = document.getElementById("m_blog").getElementsByTagName('img'); var imgw = document.getElementById("m_blog").offsetWidth; imgw =imgw-40; for(var i=0; i<imgarray.length; i++){ if(imgarray[i].className=="blogimg" && imgarray[i].width>=imgw) imgarray[i].width=imgw; }}// Fix ff bugsvar blog_text = document.getElementById('blog_text');blog_text.innerHTML = blog_text.innerHTML.replace(/href\s*=\s*("|')?(\.\.\/\.\.\/)/gi,"href=$1../$2");</SCRIPT>
</CENTER><IMG style="DISPLAY: none" src=""> </BODY></HTML>
?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -