vtrans.h

//------------------------------------------------------------------------------ // File: VTrans.h // // Desc: DirectShow base classes - defines a video transform class. // // Copyright (c) 1992-2001 Microsoft Corporation. All rights reserved. //------------------------------------------------------------------------------ // This class is derived from CTransformFilter, but is specialised to handle // the requirements of video quality control by frame dropping. // This is a non-in-place transform, (i.e. it copies the data) such as a decoder. class CVideoTransformFilter : public CTransformFilter { public: CVideoTransformFilter(__in_opt LPCTSTR, __inout_opt LPUNKNOWN, REFCLSID clsid); ~CVideoTransformFilter(); HRESULT EndFlush(); // ================================================================= // ----- override these bits --------------------------------------- // ================================================================= // The following methods are in CTransformFilter which is inherited. // They are mentioned here for completeness // // These MUST be supplied in a derived class // // NOTE: // virtual HRESULT Transform(IMediaSample * pIn, IMediaSample *pOut); // virtual HRESULT CheckInputType(const CMediaType* mtIn) PURE; // virtual HRESULT CheckTransform // (const CMediaType* mtIn, const CMediaType* mtOut) PURE; // static CCOMObject * CreateInstance(LPUNKNOWN, HRESULT *); // virtual HRESULT DecideBufferSize // (IMemAllocator * pAllocator, ALLOCATOR_PROPERTIES *pprop) PURE; // virtual HRESULT GetMediaType(int iPosition, CMediaType *pMediaType) PURE; // // These MAY also be overridden // // virtual HRESULT StopStreaming(); // virtual HRESULT SetMediaType(PIN_DIRECTION direction,const CMediaType *pmt); // virtual HRESULT CheckConnect(PIN_DIRECTION dir,IPin *pPin); // virtual HRESULT BreakConnect(PIN_DIRECTION dir); // virtual HRESULT CompleteConnect(PIN_DIRECTION direction,IPin *pReceivePin); // virtual HRESULT EndOfStream(void); // virtual HRESULT BeginFlush(void); // virtual HRESULT EndFlush(void); // virtual HRESULT NewSegment // (REFERENCE_TIME tStart,REFERENCE_TIME tStop,double dRate); #ifdef PERF // If you override this - ensure that you register all these ids // as well as any of your own, virtual void RegisterPerfId() { m_idSkip = MSR_REGISTER(TEXT("Video Transform Skip frame")); m_idFrameType = MSR_REGISTER(TEXT("Video transform frame type")); m_idLate = MSR_REGISTER(TEXT("Video Transform Lateness")); m_idTimeTillKey = MSR_REGISTER(TEXT("Video Transform Estd. time to next key")); CTransformFilter::RegisterPerfId(); } #endif protected: // =========== QUALITY MANAGEMENT IMPLEMENTATION ======================== // Frames are assumed to come in three types: // Type 1: an AVI key frame or an MPEG I frame. // This frame can be decoded with no history. // Dropping this frame means that no further frame can be decoded // until the next type 1 frame. // Type 1 frames are sync points. // Type 2: an AVI non-key frame or an MPEG P frame. // This frame cannot be decoded unless the previous type 1 frame was // decoded and all type 2 frames since have been decoded. // Dropping this frame means that no further frame can be decoded // until the next type 1 frame. // Type 3: An MPEG B frame. // This frame cannot be decoded unless the previous type 1 or 2 frame // has been decoded AND the subsequent type 1 or 2 frame has also // been decoded. (This requires decoding the frames out of sequence). // Dropping this frame affects no other frames. This implementation // does not allow for these. All non-sync-point frames are treated // as being type 2. // // The spacing of frames of type 1 in a file is not guaranteed. There MUST // be a type 1 frame at (well, near) the start of the file in order to start // decoding at all. After that there could be one every half second or so, // there could be one at the start of each scene (aka "cut", "shot") or // there could be no more at all. // If there is only a single type 1 frame then NO FRAMES CAN BE DROPPED // without losing all the rest of the movie. There is no way to tell whether // this is the case, so we find that we are in the gambling business. // To try to improve the odds, we record the greatest interval between type 1s // that we have seen and we bet on things being no worse than this in the // future. // You can tell if it's a type 1 frame by calling IsSyncPoint(). // there is no architected way to test for a type 3, so you should override // the quality management here if you have B-frames. int m_nKeyFramePeriod; // the largest observed interval between type 1 frames // 1 means every frame is type 1, 2 means every other. int m_nFramesSinceKeyFrame; // Used to count frames since the last type 1. // becomes the new m_nKeyFramePeriod if greater. BOOL m_bSkipping; // we are skipping to the next type 1 frame #ifdef PERF int m_idFrameType; // MSR id Frame type. 1=Key, 2="non-key" int m_idSkip; // MSR id skipping int m_idLate; // MSR id lateness int m_idTimeTillKey; // MSR id for guessed time till next key frame. #endif virtual HRESULT StartStreaming(); HRESULT AbortPlayback(HRESULT hr); // if something bad happens HRESULT Receive(IMediaSample *pSample); HRESULT AlterQuality(Quality q); BOOL ShouldSkipFrame(IMediaSample * pIn); int m_itrLate; // lateness from last Quality message // (this overflows at 214 secs late). int m_tDecodeStart; // timeGetTime when decode started. int m_itrAvgDecode; // Average decode time in reference units. BOOL m_bNoSkip; // debug - no skipping. // We send an EC_QUALITY_CHANGE notification to the app if we have to degrade. // We send one when we start degrading, not one for every frame, this means // we track whether we've sent one yet. BOOL m_bQualityChanged; // When non-zero, don't pass anything to renderer until next keyframe // If there are few keys, give up and eventually draw something int m_nWaitForKey; };

↑ V703 It is odd that the 'm_bQualityChanged' field in derived class 'CVideoTransformFilter' overwrites field in base class 'CTransformFilter'. Check lines: vtrans.h:138, transfrm.h:277.