Sequencer 源代码示例代码

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本主题演示在 Microsoft Media Foundation 中使用 Sequencer 源 的示例代码。 其中包含以下各节。

CPlaylist 类

类 CPlaylist 派生自 CPlayer 教程 How to Play Media Files with Media Foundation 中所示的 类。

const DWORD MAX_PLAYLIST_SEGMENTS = 128;

// For this example, there is a hard-coded limit to the number of playlist 
// segments, to avoid using a dynamically sized list.

class CPlaylist : public CPlayer
{
private:
    IMFSequencerSource     *m_pSequencerSource;
    IMFPresentationClock   *m_pPresentationClock;     

    MFTIME      m_PresentationTimeOffset;
    DWORD       m_ActiveSegment;
    LONGLONG    m_hnsSegmentDuration;

    // Table of segment IDs and topology IDs.
    struct 
    {
        MFSequencerElementId    SegmentID;
        TOPOID                    TopoID;
    } m_segments[MAX_PLAYLIST_SEGMENTS];

    DWORD m_count;

private:

    MFSequencerElementId LastSegment() const
    {
        return m_segments[ m_count - 1].SegmentID;
    }

    HRESULT LookupTopoID(TOPOID id, DWORD *pIndex);
    HRESULT OnSessionEvent(IMFMediaEvent *pEvent, MediaEventType meType);
    HRESULT OnTopologyStatus(IMFMediaEvent *pEvent);
    HRESULT OnNewPresentation(IMFMediaEvent *pEvent);
    HRESULT AddSegment(PCWSTR pszURL);
    HRESULT QueueNextSegment(IMFPresentationDescriptor *pPD);

    CPlaylist(HWND hWnd, HRESULT *phr);
    ~CPlaylist();

    HRESULT Initialize();
    
public:

    static HRESULT CreateInstance(HWND hwnd, CPlaylist **ppPlayer);

    HRESULT AddToPlaylist(PCWSTR pszURL); 
    HRESULT DeleteSegment(DWORD index);
    HRESULT SkipTo(DWORD index);

    DWORD   NumSegments() { return m_count; }
    DWORD   ActiveSegment() const { return m_ActiveSegment; }

    HRESULT GetPlaybackTime(MFTIME *phnsPresentation, MFTIME *phnsSegment);

    LONGLONG SegmentDuration() { return m_hnsSegmentDuration; }
};

创建 CPlaylist 的实例

方法 CPlaylist::CreateInstance 创建一个新的 CPlaylist 对象。 在内部，此方法调用 CPlaylist::Initialize 以初始化 对象。 方法 Initialize 调用 MFCreateSequencerSource 来创建序列源。 它还调用 IMFMediaSession：：GetClock 来获取指向表示时钟的指针。

/*static*/ 
HRESULT CPlaylist::CreateInstance(HWND hwnd, CPlaylist **ppPlayer)
{
    *ppPlayer = NULL;

    HRESULT hr = S_OK;

    CPlaylist *pPlayer = new (std::nothrow) CPlaylist(hwnd, &hr);
    if (pPlayer == NULL)
    {
        return E_OUTOFMEMORY;
    }

    if (SUCCEEDED(hr))
    {
        hr = pPlayer->Initialize();
    }

    if (SUCCEEDED(hr))
    {
        *ppPlayer = pPlayer;
    }
    else
    {
        pPlayer->Release();
    }
    return hr;
}

HRESULT CPlaylist::Initialize()
{
    IMFClock *pClock = NULL;

    HRESULT hr = CPlayer::CreateSession();
    if (FAILED(hr))
    {
        goto done;
    }

    // Create an instance of the sequencer Source.
    hr = MFCreateSequencerSource(NULL, &m_pSequencerSource);
    if (FAILED(hr))
    {
        goto done;
    }

    hr = m_pSequencerSource->QueryInterface(IID_PPV_ARGS(&m_pSource));
    if (FAILED(hr))
    {
        goto done;
    }
    
    // Get the presentation clock.
    hr = m_pSession->GetClock(&pClock);
    if (FAILED(hr))
    {
        goto done;
    }
    hr = pClock->QueryInterface(IID_PPV_ARGS(&m_pPresentationClock));

done:
    SafeRelease(&pClock);
    return hr;
}

CPlaylist::CPlaylist(HWND hWnd, HRESULT *phr)
:   CPlayer(NULL, hWnd, phr),
    m_pSequencerSource (NULL),
    m_pPresentationClock (NULL),
    m_PresentationTimeOffset (0),
    m_ActiveSegment((DWORD)-1),
    m_hnsSegmentDuration(0),
    m_count(0)
{
}

CPlaylist::~CPlaylist()
{
    SafeRelease(&m_pSequencerSource);
    SafeRelease(&m_pPresentationClock);
}

添加和删除播放列表段

方法 AddSegment 添加新的播放列表段。

此方法执行以下步骤：

  1. 创建播放拓扑。 创建 播放拓扑主题中显示了此步骤的代码。
  2. 调用 IMFSequencerSource：：AppendTopology 将拓扑添加到播放列表。
  3. 在第一个段中，获取包含播放持续时间的 MF_PD_DURATION 属性的值。
  4. 将段 ID 和拓扑 ID 存储在查阅表中。
// Adds a segment to the sequencer.

HRESULT CPlaylist::AddSegment(PCWSTR pszURL)
{
    IMFMediaSource *pMediaSource = NULL;
    IMFPresentationDescriptor *pPD = NULL;
    IMFTopology *pTopology = NULL;

    MFSequencerElementId SegmentId;
    TOPOID TopologyID = 0;
    
    HRESULT hr = CreateMediaSource(pszURL, &pMediaSource);
    if (FAILED(hr))
    {
        goto done;
    }

    hr = pMediaSource->CreatePresentationDescriptor(&pPD);
    if (FAILED(hr))
    {
        goto done;
    }

    hr = CreatePlaybackTopology(pMediaSource, pPD, m_hwndVideo, &pTopology);
    if (FAILED(hr))
    {
        goto done;
    }

    hr = m_pSequencerSource->AppendTopology(
        pTopology, 
        SequencerTopologyFlags_Last, 
        &SegmentId
        );

    if (FAILED(hr))
    {
        goto done;
    }

    hr = pTopology->GetTopologyID(&TopologyID);
    if (FAILED(hr))
    {
        goto done;
    }
        
   
    if (m_count == 0)
    {
        // Get the segment duration
        m_hnsSegmentDuration = MFGetAttributeUINT64(pPD, MF_PD_DURATION, 0);
    }

    m_segments[m_count].SegmentID = SegmentId;
    m_segments[m_count].TopoID = TopologyID;

    m_count++;

done:
    SafeRelease(&pMediaSource);
    SafeRelease(&pTopology);
    SafeRelease(&pPD);
    return hr;
}

方法 AddSegment 对 是私有的 CPlaylist，是从以下公共方法调用的：

// Adds a new segment to the playlist.

HRESULT CPlaylist::AddToPlaylist(PCWSTR pszURL)
{
    if (NumSegments() >= MAX_PLAYLIST_SEGMENTS)
    {
        return MF_E_OUT_OF_RANGE;
    }

    HRESULT hr = S_OK;

    IMFPresentationDescriptor *pPD = NULL;

    BOOL bFirstSegment = (NumSegments() == 0);

    if (!bFirstSegment)
    {
        // Remove the "last segment" flag from the last segment.
        hr = m_pSequencerSource->UpdateTopologyFlags(LastSegment(), 0);
        if (FAILED(hr))
        {
            goto done;
        }
    }

    // Create the topology and add it to the sequencer.
    hr = AddSegment(pszURL);
    if (FAILED(hr))
    {
        goto done;
    }

    // If this is the first segment, queue it on the session.
    if (bFirstSegment)
    {
        hr = m_pSource->CreatePresentationDescriptor(&pPD);
        if (FAILED(hr))
        {
            goto done;
        }

        hr = QueueNextSegment(pPD);
        if (FAILED(hr))
        {
            goto done;
        }
    }

    if (m_state < Started)
    {
        m_state = OpenPending;
    }

done:
    SafeRelease(&pPD);
    return hr;
}

创建第一个播放列表段时，必须在媒体会话中将段拓扑排队，如下所示：

  1. 查询 IMFMediaSourceTopologyProvider 接口的 sequencer 源。
  2. 将表示描述符传递给 IMFMediaSourceTopologyProvider：：GetMediaSourceTopology 方法。 此方法获取指向段拓扑的指针。 请注意，此拓扑与之前创建的播放拓扑不完全相同。 相反，它是该拓扑的修改版本。 有关详细信息，请参阅 关于 Sequencer 源。
  3. 通过调用 IMFMediaSession：：SetTopology 将媒体会话上的拓扑排队。

下面的代码演示了这些步骤。 当播放列表预滚动下一段时，也会使用此相同的代码。

// Queues the next topology on the session.

HRESULT CPlaylist::QueueNextSegment(IMFPresentationDescriptor *pPD)
{
    IMFMediaSourceTopologyProvider *pTopoProvider = NULL;
    IMFTopology *pTopology = NULL;

    //Get the topology for the presentation descriptor
    HRESULT hr = m_pSequencerSource->QueryInterface(IID_PPV_ARGS(&pTopoProvider));
    if (FAILED(hr))
    {
        goto done;
    }

    hr = pTopoProvider->GetMediaSourceTopology(pPD, &pTopology);
    if (FAILED(hr))
    {
        goto done;
    }

    //Set the topology on the media session
    m_pSession->SetTopology(NULL, pTopology);

done:
    SafeRelease(&pTopoProvider);
    SafeRelease(&pTopology);
    return hr;
}

若要删除播放列表段，请调用 IMFSequencerSource：:D eleteTopology。 段由段 ID 指定。 (这就是应用程序应缓存段 ID 列表的原因) 

// Deletes the corresponding topology from the sequencer source

HRESULT CPlaylist::DeleteSegment(DWORD index)
{
    if (index >= m_count)
    {
        return E_INVALIDARG;
    }

    if (index == m_ActiveSegment)
    {
        return E_INVALIDARG;
    }

    MFSequencerElementId LastSegId = LastSegment();
    MFSequencerElementId SegmentID = m_segments[index].SegmentID;

    HRESULT hr  = m_pSequencerSource->DeleteTopology( SegmentID );
    if (FAILED(hr))
    {
        goto done;
    }

    //Delete the segment entry from the list.

    // Move everything up one slot.
    for (DWORD i = index; i < m_count - 1; i++)
    {
        m_segments[i] = m_segments[i + 1];
    }

    m_count --;
   
    // Is the deleted topology the last one?
    if (LastSegId == SegmentID)
    {
        //Get the new last segment id
        LastSegId = LastSegment();

        //set this topology as the last in the sequencer
        hr = m_pSequencerSource->UpdateTopologyFlags(LastSegId, SequencerTopologyFlags_Last);
    }

done:
    return hr;
}

处理会话事件

HRESULT CPlaylist::OnTopologyStatus(IMFMediaEvent *pEvent)
{
    IMFTopology *pTopology = NULL;

    UINT value = 0;
    DWORD  SegmentIndex;
    TOPOID TopoID;

    HRESULT hr = pEvent->GetUINT32(MF_EVENT_TOPOLOGY_STATUS, &value);
    if (FAILED(hr))
    {
        goto done;
    }

    switch(value)
    {
    case MF_TOPOSTATUS_STARTED_SOURCE:

        // Get information about the new segment
        hr = GetEventObject(pEvent, &pTopology);
        if (FAILED(hr))
        {
            hr = S_OK;
            goto done;
        }

        hr = pTopology->GetTopologyID(&TopoID);
        if (FAILED(hr))
        {
            goto done;
        }

        hr = LookupTopoID(TopoID, &SegmentIndex);
        if (FAILED(hr))
        {
            goto done;
        }

        m_ActiveSegment = SegmentIndex;
        hr = GetDurationFromTopology(pTopology, &m_hnsSegmentDuration);
        break;

    case MF_TOPOSTATUS_ENDED:
        m_ActiveSegment = (DWORD)-1;
        break;

    case MF_TOPOSTATUS_READY:
        if (m_state == OpenPending)
        {
            m_state = Stopped;
        }
        break;
    }

done:
    SafeRelease(&pTopology);
    return hr;
}

HRESULT CPlaylist::LookupTopoID(TOPOID id, DWORD *pIndex)
{
    DWORD index;
    for (index = 0; index < m_count; index++)
    {
        if (m_segments[ index ].TopoID == id)
        {
            break;
        }
    }

    if (index == m_count)
    {
        return MF_E_NOT_FOUND;
    }

    *pIndex = index;
    return S_OK;
}

HRESULT CPlaylist::OnSessionEvent(IMFMediaEvent *pEvent, MediaEventType meType)
{
    if (meType == MESessionNotifyPresentationTime)
    {
        m_PresentationTimeOffset = 
            MFGetAttributeUINT64(pEvent, MF_EVENT_PRESENTATION_TIME_OFFSET, 0);
    }
    return S_OK;
}

HRESULT CPlaylist::OnNewPresentation(IMFMediaEvent *pEvent)
{
    IMFPresentationDescriptor *pPD = NULL;

    HRESULT hr = GetEventObject(pEvent, &pPD);

    if (SUCCEEDED(hr))
    {
        // Queue the next segment on the media session
        hr = QueueNextSegment(pPD);
    }

    SafeRelease(&pPD);
    return hr;
}

// Skips to the specified segment in the sequencer source

HRESULT CPlaylist::SkipTo(DWORD index)
{
    if (index >= m_count)
    {
        return E_INVALIDARG;
    }

    MFSequencerElementId ID = m_segments[index].SegmentID;

    PROPVARIANT var;

    HRESULT hr = MFCreateSequencerSegmentOffset(ID, NULL, &var);
    
    if (SUCCEEDED(hr))
    {
        hr = m_pSession->Start(&MF_TIME_FORMAT_SEGMENT_OFFSET, &var);
        PropVariantClear(&var);
    }
    return hr;
}

HRESULT GetDurationFromTopology(IMFTopology *pTopology, LONGLONG *phnsDuration)
{
    *phnsDuration = 0;

    IMFCollection *pSourceNodes = NULL;
    IMFTopologyNode *pNode = NULL;
    IMFPresentationDescriptor *pPD = NULL;

    HRESULT hr = pTopology->GetSourceNodeCollection(&pSourceNodes);
    if (FAILED(hr))
    {
        goto done;
    }

    hr = GetCollectionObject(pSourceNodes, 0, &pNode);
    if (FAILED(hr))
    {
        goto done;
    }
    
    hr = pNode->GetUnknown(MF_TOPONODE_PRESENTATION_DESCRIPTOR, IID_PPV_ARGS(&pPD));
    if (FAILED(hr))
    {
        goto done;
    }

    *phnsDuration = MFGetAttributeUINT64(pPD, MF_PD_DURATION, 0);

done:
    SafeRelease(&pSourceNodes);
    SafeRelease(&pNode);
    SafeRelease(&pPD);
    return hr;
}

HRESULT CPlaylist::GetPlaybackTime(
    MFTIME *phnsPresentation,    // Relative to start of presentation.
    MFTIME *phnsSegment          // Relative to start of segment.
    )
{
    *phnsPresentation = 0;
    *phnsSegment = 0;

    HRESULT hr = m_pPresentationClock->GetTime(phnsPresentation);

    if (SUCCEEDED(hr))
    {
        *phnsSegment = (*phnsPresentation) - m_PresentationTimeOffset;
    }
    return hr;
}

Sequencer 源