我有一个使用 DSPACK 组件库用 Delphi 6 编写的 DirectShow 应用程序。我有两个相互合作的过滤器图。
主过滤器图具有以下结构：
- 具有 100 ms 缓冲区大小的捕获过滤器。
- （连接到）样品采集过滤器。
“二级”过滤器图具有这种结构。
- 自定义推送源过滤器，将音频直接接收到它管理的音频缓冲区仓库。
- （连接到）渲染过滤器。
Push Source Filter 使用事件来控制音频的传递。它的 FillBuffer() 命令等待事件。当新的音频数据添加到缓冲区时，会发出事件信号。
当我运行过滤器图表时，我听到音频中有微小的“间隙”。通常我会将这种情况与构造不正确的音频缓冲区联系起来，这些缓冲区没有被填充或在其中有“间隙”。但作为测试，我添加了一个 Tee 过滤器并连接了一个 WAV Dest 过滤器，然后是一个 File Writer 过滤器。当我检查输出 WAV 文件时，它非常平滑且连续。换句话说，我从扬声器听到的间隙在输出文件中并不明显。
这表明尽管来自 Capture Filter 的音频传播成功，但音频缓冲区的传递却受到周期性干扰。我听到的“间隙”不是每秒 10 次，而是每秒 2 或 3 次，有时甚至是短时间根本没有间隙。所以不是每个缓冲区都发生这种情况，否则我会听到每秒 10 次的间隙。
我的第一个猜测是它是一个锁定问题，但我在 150 毫秒的事件上设置了超时，如果发生这种情况，则会引发异常。没有抛出异常。我还在应用程序中使用的每个关键部分设置了 40 毫秒的超时，并且这些部分都没有触发。我检查了我的 OutputDebugString() 转储以及非信号（阻塞）和信号之间的时间（未阻塞的）事件显示了在 94 毫秒和 140 毫秒之间交替的相当恒定的模式。换句话说，我的 Push Source Filter 中的 FillBuffer() 调用保持阻塞 94 毫秒，然后是 140 毫秒，然后重复。请注意持续时间有点漂移，但它很规律。考虑到 Windows 线程切换的变幻莫测，这种模式似乎与等待捕获过滤器的线程以 100 毫秒的间隔将其音频缓冲区转储到推送源过滤器的线程一致。
我想我在我的推送源过滤器中使用了双缓冲，所以我相信如果没有一个锁定机制花费 200 毫秒或更多的组合时间，我不应该中断音频流。但我想不出除了会导致这些症状的锁定问题之外的其他任何事情。我在下面的推送源过滤器中包含了我的 DecideBufferSize() 方法的代码，以防我做错了什么。虽然它有点冗长，但我还在下面包含了 FillBuffer() 调用，以显示我如何生成时间戳，以防万一可能产生影响。
尽管所有音频缓冲区都完好无损地传递，还有什么可能导致我的渲染过滤器的音频流口吃？
问题：我必须自己实现双缓冲吗？我认为 DirectShow 渲染过滤器会为您做到这一点，否则我在没有自定义推送源过滤器的情况下创建的其他过滤器图将无法正常工作。但也许因为我在过滤器图中创建了另一个锁定/解锁情况，我需要添加我自己的双缓冲层？我当然想避免这种情况以避免额外的延迟，所以如果我的情况有其他解决方法，我想知道。
function TPushSourcePinBase_wavaudio.DecideBufferSize(Allocator: IMemAllocator; Properties: PAllocatorProperties): HRESULT;
var
// pvi: PVIDEOINFOHEADER;
errMsg: string;
Actual: ALLOCATOR_PROPERTIES;
sampleSize, numBytesPerBuffer: integer;
// ourOwnerFilter: TPushSourceFilterBase_wavaudio;
begin
if (Allocator = nil) or (Properties = nil) then
begin
Result := E_POINTER;
// =========================== EXIT POINT ==============
Exit;
end; // if (Allocator = nil) or (Properties = nil) then
FFilter.StateLock.Lock;
try
// Allocate enough space for the desired amount of milliseconds
// we want to buffer (approximately).
numBytesPerBuffer := Trunc((FOurOwnerFilter.WaveFormatEx.nAvgBytesPerSec / 1000) * FBufferLatencyMS);
// Round it up to be an even multiple of the size of a sample in bytes.
sampleSize := bytesPerSample(FOurOwnerFilter.WaveFormatEx);
// Round it down to the nearest increment of sample size.
numBytesPerBuffer := (numBytesPerBuffer div sampleSize) * sampleSize;
if gDebug then OutputDebugString(PChar(
'(TPushSourcePinBase_wavaudio.DecideBufferSize) Resulting buffer size for audio is: ' + IntToStr(numBytesPerBuffer)
));
// Sanity check on the buffer size.
if numBytesPerBuffer < 1 then
begin
errMsg := '(TPushSourcePinBase_wavaudio.DecideBufferSize) The calculated number of bytes per buffer is zero or less.';
if gDebug then OutputDebugString(PChar(errMsg));
MessageBox(0, PChar(errMsg), 'PushSource Play Audio File filter error', MB_ICONERROR or MB_OK);
Result := E_FAIL;
// =========================== EXIT POINT ==============
Exit;
end;
// --------------- Do the buffer allocation -----------------
// Ensure a minimum number of buffers
if (Properties.cBuffers = 0) then
Properties.cBuffers := 2;
Properties.cbBuffer := numBytesPerBuffer;
Result := Allocator.SetProperties(Properties^, Actual);
if Failed(Result) then
// =========================== EXIT POINT ==============
Exit;
// Is this allocator unsuitable?
if (Actual.cbBuffer < Properties.cbBuffer) then
Result := E_FAIL
else
Result := S_OK;
finally
FFilter.StateLock.UnLock;
end; // try()
end;
// *******************************************************
// This is where we provide the audio data.
function TPushSourcePinBase_wavaudio.FillBuffer(Sample: IMediaSample): HResult;
// Given a Wave Format and a Byte count, convert the Byte count
// to a REFERENCE_TIME value.
function byteCountToReferenceTime(waveFormat: TWaveFormat; numBytes: LongInt): REFERENCE_TIME;
var
durationInSeconds: Extended;
begin
if waveFormat.nAvgBytesPerSec <= 0 then
raise Exception.Create('(TPushSourcePinBase_wavaudio.FillBuffer::byteCountToReferenceTime) Invalid average bytes per second value found in the wave format parameter: ' + IntToStr(waveFormat.nAvgBytesPerSec));
// Calculate the duration in seconds given the audio format and the
// number of bytes requested.
durationInSeconds := numBytes / waveFormat.nAvgBytesPerSec;
// Convert it to increments of 100ns since that is the unit value
// for DirectShow timestamps (REFERENCE_TIME).
Result :=
Trunc(durationInSeconds * REFTIME_ONE_SECOND);
end;
// ---------------------------------------------------------------
function min(v1, v2: DWord): DWord;
begin
if v1 <= v2 then
Result := v1
else
Result := v2;
end;
// ---------------------------------------------------------------
var
pData: PByte;
cbData: Longint;
pwfx: PWaveFormat;
aryOutOfDataIDs: TDynamicStringArray;
intfAudFiltNotify: IAudioFilterNotification;
i: integer;
errMsg: string;
bIsShuttingDown: boolean;
// MSDN: The REFERENCE_TIME data type defines the units for reference times
// in DirectShow. Each unit of reference time is 100 nanoseconds.
Start, Stop: REFERENCE_TIME;
durationInRefTime, ofsInRefTime: REFERENCE_TIME;
wfOutputPin: TWaveFormat;
aryDebug: TDynamicByteArray;
begin
aryDebug := nil;
if (Sample = nil) then
begin
Result := E_POINTER;
// =========================== EXIT POINT ==============
Exit;
end; // if (Sample = nil) then
// Quick lock to get sample size.
FSharedState.Lock;
try
cbData := Sample.GetSize;
finally
// Don't want to have our filter state locked when calling
// isEnoughDataOrBlock() since that call can block.
FSharedState.UnLock;
end; // try
aryOutOfDataIDs := nil;
intfAudFiltNotify := nil;
// This call will BLOCK until have enough data to satisfy the request
// or the buffer storage collection is freed.
if FOurOwnerFilter.bufferStorageCollection.isEnoughDataOrBlock(cbData, bIsShuttingDown) then
begin
// If we are shutting down, just exit with S_FALSE as the return to
// tell the caller we are done streaming.
if bIsShuttingDown then
begin
Result := S_FALSE;
// =========================== EXIT POINT ==============
exit;
end; // if bIsShuttingDown then
// Re-acquire the filter state lock.
FSharedState.Lock;
try
// Get the data and return it.
// Access the sample's data buffer
cbData := Sample.GetSize;
Sample.GetPointer(pData);
// Make sure this format matches the media type we are supporting.
pwfx := AMMediaType.pbFormat; // This is the format that our Output pin is set to.
wfOutputPin := waveFormatExToWaveFormat(FOurOwnerFilter.waveFormatEx);
if not isEqualWaveFormat(pwfx^, wfOutputPin) then
begin
Result := E_FAIL;
errMsg :=
'(TPushSourcePinBase_wavaudio.FillBuffer) The wave format of the incoming media sample does not match ours.'
+ CRLF
+ ' > Incoming sample: ' + waveFormatToString(pwfx^)
+ CRLF
+ ' > Our output pin: ' + waveFormatToString(wfOutputPin);
OutputDebugString(PChar(errMsg));
postComponentLogMessage_error(errMsg, FOurOwnerFilter.FFilterName);
MessageBox(0, PChar(errMsg), 'PushSource Play Audio File filter error', MB_ICONERROR or MB_OK);
Result := E_FAIL;
// =========================== EXIT POINT ==============
exit;
end; // if not isEqualWaveFormatEx(pwfx^, FOurOwnerFilter.waveFormatEx) then
// Convert the Byte index into the WAV data array into a reference
// time value in order to offset the start and end timestamps.
ofsInRefTime := byteCountToReferenceTime(pwfx^, FWaveByteNdx);
// Convert the number of bytes requested to a reference time vlaue.
durationInRefTime := byteCountToReferenceTime(pwfx^, cbData);
// Now I can calculate the timestamps that will govern the playback
// rate.
Start := ofsInRefTime;
Stop := Start + durationInRefTime;
{
OutputDebugString(PChar(
'(TPushSourcePinBase_wavaudio.FillBuffer) Wave byte index, start time, stop time: '
+ IntToStr(FWaveByteNdx)
+ ', '
+ IntToStr(Start)
+ ', '
+ IntToStr(Stop)
));
}
Sample.SetTime(@Start, @Stop);
// Set TRUE on every sample for uncompressed frames
Sample.SetSyncPoint(True);
// Check that we're still using audio
Assert(IsEqualGUID(AMMediaType.formattype, FORMAT_WaveFormatEx));
{
// Debugging.
FillChar(pData^, cbData, 0);
SetLength(aryDebug, cbData);
if not FOurOwnerFilter.bufferStorageCollection.mixData(@aryDebug[0], cbData, aryOutOfDataIDs) then
}
// Grab the requested number of bytes from the audio data.
if not FOurOwnerFilter.bufferStorageCollection.mixData(pData, cbData, aryOutOfDataIDs) then
begin
// We should not have had any partial copies since we
// called isEnoughDataOrBlock(), which is not supposed to
// return TRUE unless there is enough data.
Result := E_FAIL;
errMsg := '(TPushSourcePinBase_wavaudio.FillBuffer) The mix-data call returned FALSE despite our waiting for sufficient data from all participating buffer channels.';
OutputDebugString(PChar(errMsg));
postComponentLogMessage_error(errMsg, FOurOwnerFilter.FFilterName);
MessageBox(0, PChar(errMsg), 'PushSource Play Audio File filter error', MB_ICONERROR or MB_OK);
Result := E_FAIL;
// =========================== EXIT POINT ==============
exit;
end; // if not FOurOwnerFilter.bufferStorageCollection.mixData(pData, cbData, aryOutOfDataIDs) then
// ------------- OUT OF DATA NOTIFICATIONS -----------------
{
WARNING: TBufferStorageCollection automatically posts
AudioFilterNotification messages to any buffer storage
that has a IRequestStep user data interface attached to
it!.
}
if FOurOwnerFilter.wndNotify > 0 then
begin
// ----- Post Audio Notification to Filter level notify handle ---
if Length(aryOutOfDataIDs) > 0 then
begin
for i := Low(aryOutOfDataIDs) to High(aryOutOfDataIDs) do
begin
// Create a notification and post it.
intfAudFiltNotify := TAudioFilterNotification.Create(aryOutOfDataIDs[i], afnOutOfData);
// ourOwnerFilter.intfNotifyRequestStep.triggerResult(intfAudFiltNotify);
PostMessageWithUserDataIntf(FOurOwnerFilter.wndNotify, WM_PUSH_SOURCE_FILTER_NOTIFY, intfAudFiltNotify);
end; // for()
end; // if Length(aryOutOfDataIDs) > 0 then
end; // if FOurOwnerFilter.wndNotify > 0 then
// Advance the Wave Byte index by the number of bytes requested.
Inc(FWaveByteNdx, cbData);
Result := S_OK;
finally
FSharedState.UnLock;
end; // try
end
else
begin
// Tell DirectShow to stop streaming with us. Something has
// gone seriously wrong with the audio streams feeding us.
errMsg := '(TPushSourcePinBase_wavaudio.FillBuffer) Time-out occurred while waiting for sufficient data to accumulate in our audio buffer channels.';
OutputDebugString(PChar(errMsg));
postComponentLogMessage_error(errMsg, FFilter.filterName);
MessageBox(0, PChar(errMsg), 'PushSource Play Audio File filter error', MB_ICONERROR or MB_OK);
Result := E_FAIL;
end;
end;
