LAV Filter 源代码分析 4： LAV Video （2）

上一篇文章分析了LAV Filter 中的LAV Video的两个主要的类：CLAVVideo和CDecodeThread。文章：LAV Filter 源代码分析 3： LAV Video （1）

在这里继续上篇文章的内容。文章中提到LAVVideo主要通过CDecodeThread这个类进行解码线程的管理，其中有一个关键的管理函数：ThreadProc()，包含了对解码线程的各种操作。函数如下所示：

//包含了对进程的各种操作
DWORD CDecodeThread::ThreadProc()
{
HRESULT hr;
DWORD cmd;

BOOL bEOS = FALSE;
BOOL bReinit = FALSE;

SetThreadName(-1, "LAVVideo Decode Thread");

HANDLE hWaitEvents[2] = { GetRequestHandle(), m_evInput };
//不停转圈，永不休止
while(1) {
if (!bEOS && !bReinit) {
// Wait for either an input sample, or an request
WaitForMultipleObjects(2, hWaitEvents, FALSE, INFINITE);
}
//根据操作命令的不同
if (CheckRequest(&cmd)) {
switch (cmd) {
//创建解码器
case CMD_CREATE_DECODER:
{
CAutoLock lock(&m_ThreadCritSec);
//创建
hr = CreateDecoderInternal(m_ThreadCallContext.pmt, m_ThreadCallContext.codec);
Reply(hr);

m_ThreadCallContext.pmt = NULL;
}
break;
case CMD_CLOSE_DECODER:
{
//关闭
ClearQueues();
SAFE_DELETE(m_pDecoder);
Reply(S_OK);
}
break;
case CMD_FLUSH:
{
//清楚
ClearQueues();
m_pDecoder->Flush();
Reply(S_OK);
}
break;
case CMD_EOS:
{
bEOS = TRUE;
m_evEOSDone.Reset();
Reply(S_OK);
}
break;
case CMD_EXIT:
{
//退出
Reply(S_OK);
return 0;
}
break;
case CMD_INIT_ALLOCATOR:
{
CAutoLock lock(&m_ThreadCritSec);
hr = m_pDecoder->InitAllocator(m_ThreadCallContext.allocator);
Reply(hr);

m_ThreadCallContext.allocator = NULL;
}
break;
case CMD_POST_CONNECT:
{
CAutoLock lock(&m_ThreadCritSec);
hr = PostConnectInternal(m_ThreadCallContext.pin);
Reply(hr);

m_ThreadCallContext.pin = NULL;
}
break;
case CMD_REINIT:
{
//重启
CMediaType &mt = m_pLAVVideo->GetInputMediaType();
CreateDecoderInternal(&mt, m_Codec);
m_TempSample[1] = m_NextSample;
m_NextSample = m_FailedSample;
m_FailedSample = NULL;
bReinit = TRUE;
m_evEOSDone.Reset();
Reply(S_OK);
m_bDecoderNeedsReInit = FALSE;
}
break;
default:
ASSERT(0);
}
}

if (m_bDecoderNeedsReInit) {
m_evInput.Reset();
continue;
}

if (bReinit && !m_NextSample) {
if (m_TempSample[0]) {
m_NextSample = m_TempSample[0];
m_TempSample[0] = NULL;
} else if (m_TempSample[1]) {
m_NextSample = m_TempSample[1];
m_TempSample[1] = NULL;
} else {
bReinit = FALSE;
m_evEOSDone.Set();
m_evSample.Set();
continue;
}
}
//获得一份数据
IMediaSample *pSample = GetSample();
if (!pSample) {
// Process the EOS now that the sample queue is empty
if (bEOS) {
bEOS = FALSE;
m_pDecoder->EndOfStream();
m_evEOSDone.Set();
m_evSample.Set();
}
continue;
}
//解码
DecodeInternal(pSample);

// Release the sample
//释放
SafeRelease(&pSample);

// Indicates we're done decoding this sample
m_evDecodeDone.Set();

// Set the Sample Event to unblock any waiting threads
m_evSample.Set();
}

return 0;
}

该函数中，DecodeInternal(pSample)为实际上真正具有解码功能的函数，来看看它的源代码吧：

STDMETHODIMP CDecodeThread::DecodeInternal(IMediaSample *pSample)
{
HRESULT hr = S_OK;

if (!m_pDecoder)
return E_UNEXPECTED;
//调用接口进行解码
hr = m_pDecoder->Decode(pSample);

// If a hardware decoder indicates a hard failure, we switch back to software
// This is used to indicate incompatible media
if (FAILED(hr) && m_bHWDecoder) {
DbgLog((LOG_TRACE, 10, L"::Receive(): Hardware decoder indicates failure, switching back to software"));
m_bHWDecoderFailed = TRUE;

// Store the failed sample for re-try in a moment
m_FailedSample = pSample;
m_FailedSample->AddRef();

// Schedule a re-init when the main thread goes there the next time
m_bDecoderNeedsReInit = TRUE;

// Make room in the sample buffer, to ensure the main thread can get in
m_TempSample[0] = GetSample();
}

return S_OK;
}

该函数比较简短，从源代码中可以看出，调用了
m_pDecoder的Decode()方法。其中
m_pDecoder为
ILAVDecoder类型的指针，而ILAVDecoder是一个接口，并不包含实际的方法，如下所示。注意，从程序注释中可以看出，每一个解码器都需要实现该接口规定的函数。

/**
* Decoder interface
*
* Every decoder needs to implement this to interface with the LAV Video core
*/
//接口
interface ILAVDecoder
{
/**
* Virtual destructor
*/
virtual ~ILAVDecoder(void) {};

/**
* Initialize interfaces with the LAV Video core
* This function should also be used to create all interfaces with external DLLs
*
* @param pSettings reference to the settings interface
* @param pCallback reference to the callback interface
* @return S_OK on success, error code if this decoder is lacking an external support dll
*/
STDMETHOD(InitInterfaces)(ILAVVideoSettings *pSettings, ILAVVideoCallback *pCallback) PURE;

/**
* Check if the decoder is functional
*/
STDMETHOD(Check)() PURE;

/**
* Initialize the codec to decode a stream specified by codec and pmt.
*
* @param codec Codec Id
* @param pmt DirectShow Media Type
* @return S_OK on success, an error code otherwise
*/
STDMETHOD(InitDecoder)(AVCodecID codec, const CMediaType *pmt) PURE;

/**
* Decode a frame.
*
* @param pSample Media Sample to decode
* @return S_OK if decoding was successfull, S_FALSE if no frame could be extracted, an error code if the decoder is not compatible with the bitstream
*
* Note: When returning an actual error code, the filter will switch to the fallback software decoder! This should only be used for catastrophic failures,
* like trying to decode a unsupported format on a hardware decoder.
*/
STDMETHOD(Decode)(IMediaSample *pSample) PURE;

/**
* Flush the decoder after a seek.
* The decoder should discard any remaining data.
*
* @return unused
*/
STDMETHOD(Flush)() PURE;

/**
* End of Stream
* The decoder is asked to output any buffered frames for immediate delivery
*
* @return unused
*/
STDMETHOD(EndOfStream)() PURE;

/**
* Query the decoder for the current pixel format
* Mostly used by the media type creation logic before playback starts
*
* @return the pixel format used in the decoding process
*/
STDMETHOD(GetPixelFormat)(LAVPixelFormat *pPix, int *pBpp) PURE;

/**
* Get the frame duration.
*
* This function is not mandatory, and if you cannot provide any specific duration, return 0.
*/
STDMETHOD_(REFERENCE_TIME, GetFrameDuration)() PURE;

/**
* Query whether the format can potentially be interlaced.
* This function should return false if the format can 100% not be interlaced, and true if it can be interlaced (but also progressive).
*/
STDMETHOD_(BOOL, IsInterlaced)() PURE;

/**
* Allows the decoder to handle an allocator.
* Used by DXVA2 decoding
*/
STDMETHOD(InitAllocator)(IMemAllocator **ppAlloc) PURE;

/**
* Function called after connection is established, with the pin as argument
*/
STDMETHOD(PostConnect)(IPin *pPin) PURE;

/**
* Get the number of sample buffers optimal for this decoder
*/
STDMETHOD_(long, GetBufferCount)() PURE;

/**
* Get the name of the decoder
*/
STDMETHOD_(const WCHAR*, GetDecoderName)() PURE;

/**
* Get whether the decoder outputs thread-safe buffers
*/
STDMETHOD(HasThreadSafeBuffers)() PURE;

/**
* Get whether the decoder should sync to the main thread
*/
STDMETHOD(SyncToProcessThread)() PURE;
};

下面来看看封装libavcodec库的类吧，该类的定义位于decoders文件夹下，名为avcodec.h，如图所示：



该类名字叫CDecAvcodec，其继承了CDecBase。而CDecBase继承了ILAVDecoder。

/* 雷霄骅
* 中国传媒大学/数字电视技术
* leixiaohua1020@126.com
*
*/
/*
*      Copyright (C) 2010-2013 Hendrik Leppkes
*      http://www.1f0.de *
*  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; either version 2 of the License, or
*  (at your option) any later version.
*
*  This program is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  You should have received a copy of the GNU General Public License along
*  with this program; if not, write to the Free Software Foundation, Inc.,
*  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

#pragma once

#include "DecBase.h"
#include "H264RandomAccess.h"

#include <map>

#define AVCODEC_MAX_THREADS 16

typedef struct {
REFERENCE_TIME rtStart;
REFERENCE_TIME rtStop;
} TimingCache;
//解码器（AVCODEC）（其实还有WMV9，CUVID等）
class CDecAvcodec : public CDecBase
{
public:
CDecAvcodec(void);
virtual ~CDecAvcodec(void);

// ILAVDecoder
STDMETHODIMP InitDecoder(AVCodecID codec, const CMediaType *pmt);
//解码
STDMETHODIMP Decode(const BYTE *buffer, int buflen, REFERENCE_TIME rtStart, REFERENCE_TIME rtStop, BOOL bSyncPoint, BOOL bDiscontinuity);
STDMETHODIMP Flush();
STDMETHODIMP EndOfStream();
STDMETHODIMP GetPixelFormat(LAVPixelFormat *pPix, int *pBpp);
STDMETHODIMP_(REFERENCE_TIME) GetFrameDuration();
STDMETHODIMP_(BOOL) IsInterlaced();
STDMETHODIMP_(const WCHAR*) GetDecoderName() { return L"avcodec"; }
STDMETHODIMP HasThreadSafeBuffers() { return S_OK; }
STDMETHODIMP SyncToProcessThread() { return m_pAVCtx && m_pAVCtx->thread_count > 1 ? S_OK : S_FALSE; }

// CDecBase
STDMETHODIMP Init();

protected:
virtual HRESULT AdditionaDecoderInit() { return S_FALSE; }
virtual HRESULT PostDecode() { return S_FALSE; }
virtual HRESULT HandleDXVA2Frame(LAVFrame *pFrame) { return S_FALSE; }
//销毁解码器，各种Free
STDMETHODIMP DestroyDecoder();

private:
STDMETHODIMP ConvertPixFmt(AVFrame *pFrame, LAVFrame *pOutFrame);

protected:
AVCodecContext       *m_pAVCtx;
AVFrame              *m_pFrame;
AVCodecID            m_nCodecId;
BOOL                 m_bDXVA;

private:
AVCodec              *m_pAVCodec;
AVCodecParserContext *m_pParser;

BYTE                 *m_pFFBuffer;
BYTE                 *m_pFFBuffer2;
int                  m_nFFBufferSize;
int                  m_nFFBufferSize2;

SwsContext           *m_pSwsContext;

CH264RandomAccess    m_h264RandomAccess;

BOOL                 m_bNoBufferConsumption;
BOOL                 m_bHasPalette;

// Timing settings
BOOL                 m_bFFReordering;
BOOL                 m_bCalculateStopTime;
BOOL                 m_bRVDropBFrameTimings;
BOOL                 m_bInputPadded;

BOOL                 m_bBFrameDelay;
TimingCache          m_tcBFrameDelay[2];
int                  m_nBFramePos;

TimingCache          m_tcThreadBuffer[AVCODEC_MAX_THREADS];
int                  m_CurrentThread;

REFERENCE_TIME       m_rtStartCache;
BOOL                 m_bResumeAtKeyFrame;
BOOL                 m_bWaitingForKeyFrame;
int                  m_iInterlaced;
};

从
CDecAvcodec类的定义可以看出，包含了各种功能的函数。首先我们看看初始化函数Init()

// ILAVDecoder
STDMETHODIMP CDecAvcodec::Init()
{
#ifdef DEBUG
DbgSetModuleLevel (LOG_CUSTOM1, DWORD_MAX); // FFMPEG messages use custom1
av_log_set_callback(lavf_log_callback);
#else
av_log_set_callback(NULL);
#endif
//注册
avcodec_register_all();
return S_OK;
}

可见其调用了ffmpeg的API函数avcodec_register_all()进行了解码器的注册。

我们再来看看其解码函数Decode()：

//解码
STDMETHODIMP CDecAvcodec::Decode(const BYTE *buffer, int buflen, REFERENCE_TIME rtStartIn, REFERENCE_TIME rtStopIn, BOOL bSyncPoint, BOOL bDiscontinuity)
{
int     got_picture = 0;
int     used_bytes  = 0;
BOOL    bParserFrame = FALSE;
BOOL    bFlush = (buffer == NULL);
BOOL    bEndOfSequence = FALSE;
//初始化Packet
AVPacket avpkt;
av_init_packet(&avpkt);

if (m_pAVCtx->active_thread_type & FF_THREAD_FRAME) {
if (!m_bFFReordering) {
m_tcThreadBuffer[m_CurrentThread].rtStart = rtStartIn;
m_tcThreadBuffer[m_CurrentThread].rtStop  = rtStopIn;
}

m_CurrentThread = (m_CurrentThread + 1) % m_pAVCtx->thread_count;
} else if (m_bBFrameDelay) {
m_tcBFrameDelay[m_nBFramePos].rtStart = rtStartIn;
m_tcBFrameDelay[m_nBFramePos].rtStop = rtStopIn;
m_nBFramePos = !m_nBFramePos;
}

uint8_t *pDataBuffer = NULL;
if (!bFlush && buflen > 0) {
if (!m_bInputPadded && (!(m_pAVCtx->active_thread_type & FF_THREAD_FRAME) || m_pParser)) {
// Copy bitstream into temporary buffer to ensure overread protection
// Verify buffer size
if (buflen > m_nFFBufferSize) {
m_nFFBufferSize	= buflen;
m_pFFBuffer = (BYTE *)av_realloc_f(m_pFFBuffer, m_nFFBufferSize + FF_INPUT_BUFFER_PADDING_SIZE, 1);
if (!m_pFFBuffer) {
m_nFFBufferSize = 0;
return E_OUTOFMEMORY;
}
}

memcpy(m_pFFBuffer, buffer, buflen);
memset(m_pFFBuffer+buflen, 0, FF_INPUT_BUFFER_PADDING_SIZE);
pDataBuffer = m_pFFBuffer;
} else {
pDataBuffer = (uint8_t *)buffer;
}

if (m_nCodecId == AV_CODEC_ID_H264) {
BOOL bRecovered = m_h264RandomAccess.searchRecoveryPoint(pDataBuffer, buflen);
if (!bRecovered) {
return S_OK;
}
} else if (m_nCodecId == AV_CODEC_ID_VP8 && m_bWaitingForKeyFrame) {
if (!(pDataBuffer[0] & 1)) {
DbgLog((LOG_TRACE, 10, L"::Decode(): Found VP8 key-frame, resuming decoding"));
m_bWaitingForKeyFrame = FALSE;
} else {
return S_OK;
}
}
}

while (buflen > 0 || bFlush) {
REFERENCE_TIME rtStart = rtStartIn, rtStop = rtStopIn;

if (!bFlush) {
//设置AVPacket中的数据
avpkt.data = pDataBuffer;
avpkt.size = buflen;
avpkt.pts = rtStartIn;
if (rtStartIn != AV_NOPTS_VALUE && rtStopIn != AV_NOPTS_VALUE)
avpkt.duration = (int)(rtStopIn - rtStartIn);
else
avpkt.duration = 0;
avpkt.flags = AV_PKT_FLAG_KEY;

if (m_bHasPalette) {
m_bHasPalette = FALSE;
uint32_t *pal = (uint32_t *)av_packet_new_side_data(&avpkt, AV_PKT_DATA_PALETTE, AVPALETTE_SIZE);
int pal_size = FFMIN((1 << m_pAVCtx->bits_per_coded_sample) << 2, m_pAVCtx->extradata_size);
uint8_t *pal_src = m_pAVCtx->extradata + m_pAVCtx->extradata_size - pal_size;

for (int i = 0; i < pal_size/4; i++)
pal[i] = 0xFF<<24 | AV_RL32(pal_src+4*i);
}
} else {
avpkt.data = NULL;
avpkt.size = 0;
}

// Parse the data if a parser is present
// This is mandatory for MPEG-1/2
// 不一定需要
if (m_pParser) {
BYTE *pOut = NULL;
int pOut_size = 0;

used_bytes = av_parser_parse2(m_pParser, m_pAVCtx, &pOut, &pOut_size, avpkt.data, avpkt.size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);

if (used_bytes == 0 && pOut_size == 0 && !bFlush) {
DbgLog((LOG_TRACE, 50, L"::Decode() - could not process buffer, starving?"));
break;
}

// Update start time cache
// If more data was read then output, update the cache (incomplete frame)
// If output is bigger, a frame was completed, update the actual rtStart with the cached value, and then overwrite the cache
if (used_bytes > pOut_size) {
if (rtStartIn != AV_NOPTS_VALUE)
m_rtStartCache = rtStartIn;
} else if (used_bytes == pOut_size || ((used_bytes + 9) == pOut_size)) {
// Why +9 above?
// Well, apparently there are some broken MKV muxers that like to mux the MPEG-2 PICTURE_START_CODE block (which is 9 bytes) in the package with the previous frame
// This would cause the frame timestamps to be delayed by one frame exactly, and cause timestamp reordering to go wrong.
// So instead of failing on those samples, lets just assume that 9 bytes are that case exactly.
m_rtStartCache = rtStartIn = AV_NOPTS_VALUE;
} else if (pOut_size > used_bytes) {
rtStart = m_rtStartCache;
m_rtStartCache = rtStartIn;
// The value was used once, don't use it for multiple frames, that ends up in weird timings
rtStartIn = AV_NOPTS_VALUE;
}

bParserFrame = (pOut_size > 0);

if (pOut_size > 0 || bFlush) {

if (pOut && pOut_size > 0) {
if (pOut_size > m_nFFBufferSize2) {
m_nFFBufferSize2	= pOut_size;
m_pFFBuffer2 = (BYTE *)av_realloc_f(m_pFFBuffer2, m_nFFBufferSize2 + FF_INPUT_BUFFER_PADDING_SIZE, 1);
if (!m_pFFBuffer2) {
m_nFFBufferSize2 = 0;
return E_OUTOFMEMORY;
}
}
memcpy(m_pFFBuffer2, pOut, pOut_size);
memset(m_pFFBuffer2+pOut_size, 0, FF_INPUT_BUFFER_PADDING_SIZE);

avpkt.data = m_pFFBuffer2;
avpkt.size = pOut_size;
avpkt.pts = rtStart;
avpkt.duration = 0;

const uint8_t *eosmarker = CheckForEndOfSequence(m_nCodecId, avpkt.data, avpkt.size, &m_MpegParserState);
if (eosmarker) {
bEndOfSequence = TRUE;
}
} else {
avpkt.data = NULL;
avpkt.size = 0;
}
//真正的解码
int ret2 = avcodec_decode_video2 (m_pAVCtx, m_pFrame, &got_picture, &avpkt);
if (ret2 < 0) {
DbgLog((LOG_TRACE, 50, L"::Decode() - decoding failed despite successfull parsing"));
got_picture = 0;
}
} else {
got_picture = 0;
}
} else {
used_bytes = avcodec_decode_video2 (m_pAVCtx, m_pFrame, &got_picture, &avpkt);
}

if (FAILED(PostDecode())) {
av_frame_unref(m_pFrame);
return E_FAIL;
}

// Decoding of this frame failed ... oh well!
if (used_bytes < 0) {
av_frame_unref(m_pFrame);
return S_OK;
}

// When Frame Threading, we won't know how much data has been consumed, so it by default eats everything.
// In addition, if no data got consumed, and no picture was extracted, the frame probably isn't all that useufl.
// The MJPEB decoder is somewhat buggy and doesn't let us know how much data was consumed really...
if ((!m_pParser && (m_pAVCtx->active_thread_type & FF_THREAD_FRAME || (!got_picture && used_bytes == 0))) || m_bNoBufferConsumption || bFlush) {
buflen = 0;
} else {
buflen -= used_bytes;
pDataBuffer += used_bytes;
}

// Judge frame usability
// This determines if a frame is artifact free and can be delivered
// For H264 this does some wicked magic hidden away in the H264RandomAccess class
// MPEG-2 and VC-1 just wait for a keyframe..
if (m_nCodecId == AV_CODEC_ID_H264 && (bParserFrame || !m_pParser || got_picture)) {
m_h264RandomAccess.judgeFrameUsability(m_pFrame, &got_picture);
} else if (m_bResumeAtKeyFrame) {
if (m_bWaitingForKeyFrame && got_picture) {
if (m_pFrame->key_frame) {
DbgLog((LOG_TRACE, 50, L"::Decode() - Found Key-Frame, resuming decoding at %I64d", m_pFrame->pkt_pts));
m_bWaitingForKeyFrame = FALSE;
} else {
got_picture = 0;
}
}
}

// Handle B-frame delay for frame threading codecs
if ((m_pAVCtx->active_thread_type & FF_THREAD_FRAME) && m_bBFrameDelay) {
m_tcBFrameDelay[m_nBFramePos] = m_tcThreadBuffer[m_CurrentThread];
m_nBFramePos = !m_nBFramePos;
}

if (!got_picture || !m_pFrame->data[0]) {
if (!avpkt.size)
bFlush = FALSE; // End flushing, no more frames
av_frame_unref(m_pFrame);
continue;
}

///////////////////////////////////////////////////////////////////////////////////////////////
// Determine the proper timestamps for the frame, based on different possible flags.
///////////////////////////////////////////////////////////////////////////////////////////////
if (m_bFFReordering) {
rtStart = m_pFrame->pkt_pts;
if (m_pFrame->pkt_duration)
rtStop = m_pFrame->pkt_pts + m_pFrame->pkt_duration;
else
rtStop = AV_NOPTS_VALUE;
} else if (m_bBFrameDelay && m_pAVCtx->has_b_frames) {
rtStart = m_tcBFrameDelay[m_nBFramePos].rtStart;
rtStop  = m_tcBFrameDelay[m_nBFramePos].rtStop;
} else if (m_pAVCtx->active_thread_type & FF_THREAD_FRAME) {
unsigned index = m_CurrentThread;
rtStart = m_tcThreadBuffer[index].rtStart;
rtStop  = m_tcThreadBuffer[index].rtStop;
}

if (m_bRVDropBFrameTimings && m_pFrame->pict_type == AV_PICTURE_TYPE_B) {
rtStart = AV_NOPTS_VALUE;
}

if (m_bCalculateStopTime)
rtStop = AV_NOPTS_VALUE;

///////////////////////////////////////////////////////////////////////////////////////////////
// All required values collected, deliver the frame
///////////////////////////////////////////////////////////////////////////////////////////////
LAVFrame *pOutFrame = NULL;
AllocateFrame(&pOutFrame);

AVRational display_aspect_ratio;
int64_t num = (int64_t)m_pFrame->sample_aspect_ratio.num * m_pFrame->width;
int64_t den = (int64_t)m_pFrame->sample_aspect_ratio.den * m_pFrame->height;
av_reduce(&display_aspect_ratio.num, &display_aspect_ratio.den, num, den, 1 << 30);

pOutFrame->width        = m_pFrame->width;
pOutFrame->height       = m_pFrame->height;
pOutFrame->aspect_ratio = display_aspect_ratio;
pOutFrame->repeat       = m_pFrame->repeat_pict;
pOutFrame->key_frame    = m_pFrame->key_frame;
pOutFrame->frame_type   = av_get_picture_type_char(m_pFrame->pict_type);
pOutFrame->ext_format   = GetDXVA2ExtendedFlags(m_pAVCtx, m_pFrame);

if (m_pFrame->interlaced_frame || (!m_pAVCtx->progressive_sequence && (m_nCodecId == AV_CODEC_ID_H264 || m_nCodecId == AV_CODEC_ID_MPEG2VIDEO)))
m_iInterlaced = 1;
else if (m_pAVCtx->progressive_sequence)
m_iInterlaced = 0;

pOutFrame->interlaced   = (m_pFrame->interlaced_frame || (m_iInterlaced == 1 && m_pSettings->GetDeinterlacingMode() == DeintMode_Aggressive) || m_pSettings->GetDeinterlacingMode() == DeintMode_Force) && !(m_pSettings->GetDeinterlacingMode() == DeintMode_Disable);

LAVDeintFieldOrder fo   = m_pSettings->GetDeintFieldOrder();
pOutFrame->tff          = (fo == DeintFieldOrder_Auto) ? m_pFrame->top_field_first : (fo == DeintFieldOrder_TopFieldFirst);

pOutFrame->rtStart      = rtStart;
pOutFrame->rtStop       = rtStop;

PixelFormatMapping map  = getPixFmtMapping((AVPixelFormat)m_pFrame->format);
pOutFrame->format       = map.lavpixfmt;
pOutFrame->bpp          = map.bpp;

if (m_nCodecId == AV_CODEC_ID_MPEG2VIDEO || m_nCodecId == AV_CODEC_ID_MPEG1VIDEO)
pOutFrame->avgFrameDuration = GetFrameDuration();

if (map.conversion) {
ConvertPixFmt(m_pFrame, pOutFrame);
} else {
for (int i = 0; i < 4; i++) {
pOutFrame->data[i]   = m_pFrame->data[i];
pOutFrame->stride[i] = m_pFrame->linesize[i];
}

pOutFrame->priv_data = av_frame_alloc();
av_frame_ref((AVFrame *)pOutFrame->priv_data, m_pFrame);
pOutFrame->destruct  = lav_avframe_free;
}

if (bEndOfSequence)
pOutFrame->flags |= LAV_FRAME_FLAG_END_OF_SEQUENCE;

if (pOutFrame->format == LAVPixFmt_DXVA2) {
pOutFrame->data[0] = m_pFrame->data[4];
HandleDXVA2Frame(pOutFrame);
} else {
Deliver(pOutFrame);
}

if (bEndOfSequence) {
bEndOfSequence = FALSE;
if (pOutFrame->format == LAVPixFmt_DXVA2) {
HandleDXVA2Frame(m_pCallback->GetFlushFrame());
} else {
Deliver(m_pCallback->GetFlushFrame());
}
}

if (bFlush) {
m_CurrentThread = (m_CurrentThread + 1) % m_pAVCtx->thread_count;
}
av_frame_unref(m_pFrame);
}

return S_OK;
}

终于，我们从这个函数中看到了很多的ffmpeg的API，结构体，以及变量。比如解码视频的函数avcodec_decode_video2()。

解码器初始化函数：InitDecoder()

//创建解码器
STDMETHODIMP CDecAvcodec::InitDecoder(AVCodecID codec, const CMediaType *pmt)
{
//要是有，先销毁
DestroyDecoder();
DbgLog((LOG_TRACE, 10, L"Initializing ffmpeg for codec %S", avcodec_get_name(codec)));

BITMAPINFOHEADER *pBMI = NULL;
videoFormatTypeHandler((const BYTE *)pmt->Format(), pmt->FormatType(), &pBMI);
//查找解码器
m_pAVCodec = avcodec_find_decoder(codec);
CheckPointer(m_pAVCodec, VFW_E_UNSUPPORTED_VIDEO);
//初始化上下文环境
m_pAVCtx = avcodec_alloc_context3(m_pAVCodec);
CheckPointer(m_pAVCtx, E_POINTER);

if(codec == AV_CODEC_ID_MPEG1VIDEO || codec == AV_CODEC_ID_MPEG2VIDEO || pmt->subtype == FOURCCMap(MKTAG('H','2','6','4')) || pmt->subtype == FOURCCMap(MKTAG('h','2','6','4'))) {
m_pParser = av_parser_init(codec);
}

DWORD dwDecFlags = m_pCallback->GetDecodeFlags();

LONG biRealWidth = pBMI->biWidth, biRealHeight = pBMI->biHeight;
if (pmt->formattype == FORMAT_VideoInfo || pmt->formattype == FORMAT_MPEGVideo) {
VIDEOINFOHEADER *vih = (VIDEOINFOHEADER *)pmt->Format();
if (vih->rcTarget.right != 0 && vih->rcTarget.bottom != 0) {
biRealWidth  = vih->rcTarget.right;
biRealHeight = vih->rcTarget.bottom;
}
} else if (pmt->formattype == FORMAT_VideoInfo2 || pmt->formattype == FORMAT_MPEG2Video) {
VIDEOINFOHEADER2 *vih2 = (VIDEOINFOHEADER2 *)pmt->Format();
if (vih2->rcTarget.right != 0 && vih2->rcTarget.bottom != 0) {
biRealWidth  = vih2->rcTarget.right;
biRealHeight = vih2->rcTarget.bottom;
}
}
//各种赋值
m_pAVCtx->codec_id              = codec;
m_pAVCtx->codec_tag             = pBMI->biCompression;
m_pAVCtx->coded_width           = pBMI->biWidth;
m_pAVCtx->coded_height          = abs(pBMI->biHeight);
m_pAVCtx->bits_per_coded_sample = pBMI->biBitCount;
m_pAVCtx->error_concealment     = FF_EC_GUESS_MVS | FF_EC_DEBLOCK;
m_pAVCtx->err_recognition       = AV_EF_CAREFUL;
m_pAVCtx->workaround_bugs       = FF_BUG_AUTODETECT;
m_pAVCtx->refcounted_frames     = 1;

if (codec == AV_CODEC_ID_H264)
m_pAVCtx->flags2             |= CODEC_FLAG2_SHOW_ALL;

// Setup threading
int thread_type = getThreadFlags(codec);
if (thread_type) {
// Thread Count. 0 = auto detect
int thread_count = m_pSettings->GetNumThreads();
if (thread_count == 0) {
thread_count = av_cpu_count() * 3 / 2;
}

m_pAVCtx->thread_count = max(1, min(thread_count, AVCODEC_MAX_THREADS));
m_pAVCtx->thread_type = thread_type;
} else {
m_pAVCtx->thread_count = 1;
}

if (dwDecFlags & LAV_VIDEO_DEC_FLAG_NO_MT) {
m_pAVCtx->thread_count = 1;
}
//初始化AVFrame
m_pFrame = av_frame_alloc();
CheckPointer(m_pFrame, E_POINTER);

m_h264RandomAccess.SetAVCNALSize(0);

// Process Extradata
//处理ExtraData
BYTE *extra = NULL;
size_t extralen = 0;
getExtraData(*pmt, NULL, &extralen);

BOOL bH264avc = FALSE;
if (extralen > 0) {
DbgLog((LOG_TRACE, 10, L"-> Processing extradata of %d bytes", extralen));
// Reconstruct AVC1 extradata format
if (pmt->formattype == FORMAT_MPEG2Video && (m_pAVCtx->codec_tag == MAKEFOURCC('a','v','c','1') || m_pAVCtx->codec_tag == MAKEFOURCC('A','V','C','1') || m_pAVCtx->codec_tag == MAKEFOURCC('C','C','V','1'))) {
MPEG2VIDEOINFO *mp2vi = (MPEG2VIDEOINFO *)pmt->Format();
extralen += 7;
extra = (uint8_t *)av_mallocz(extralen + FF_INPUT_BUFFER_PADDING_SIZE);
extra[0] = 1;
extra[1] = (BYTE)mp2vi->dwProfile;
extra[2] = 0;
extra[3] = (BYTE)mp2vi->dwLevel;
extra[4] = (BYTE)(mp2vi->dwFlags ? mp2vi->dwFlags : 4) - 1;

// Actually copy the metadata into our new buffer
size_t actual_len;
getExtraData(*pmt, extra+6, &actual_len);

// Count the number of SPS/PPS in them and set the length
// We'll put them all into one block and add a second block with 0 elements afterwards
// The parsing logic does not care what type they are, it just expects 2 blocks.
BYTE *p = extra+6, *end = extra+6+actual_len;
BOOL bSPS = FALSE, bPPS = FALSE;
int count = 0;
while (p+1 < end) {
unsigned len = (((unsigned)p[0] << 8) | p[1]) + 2;
if (p + len > end) {
break;
}
if ((p[2] & 0x1F) == 7)
bSPS = TRUE;
if ((p[2] & 0x1F) == 8)
bPPS = TRUE;
count++;
p += len;
}
extra[5] = count;
extra[extralen-1] = 0;

bH264avc = TRUE;
m_h264RandomAccess.SetAVCNALSize(mp2vi->dwFlags);
} else if (pmt->subtype == MEDIASUBTYPE_LAV_RAWVIDEO) {
if (extralen < sizeof(m_pAVCtx->pix_fmt)) {
DbgLog((LOG_TRACE, 10, L"-> LAV RAW Video extradata is missing.."));
} else {
extra = (uint8_t *)av_mallocz(extralen + FF_INPUT_BUFFER_PADDING_SIZE);
getExtraData(*pmt, extra, NULL);
m_pAVCtx->pix_fmt = *(AVPixelFormat *)extra;
extralen -= sizeof(AVPixelFormat);
memmove(extra, extra+sizeof(AVPixelFormat), extralen);
}
} else {
// Just copy extradata for other formats
extra = (uint8_t *)av_mallocz(extralen + FF_INPUT_BUFFER_PADDING_SIZE);
getExtraData(*pmt, extra, NULL);
}
// Hack to discard invalid MP4 metadata with AnnexB style video
if (codec == AV_CODEC_ID_H264 && !bH264avc && extra[0] == 1) {
av_freep(&extra);
extralen = 0;
}
m_pAVCtx->extradata = extra;
m_pAVCtx->extradata_size = (int)extralen;
} else {
if (codec == AV_CODEC_ID_VP6 || codec == AV_CODEC_ID_VP6A || codec == AV_CODEC_ID_VP6F) {
int cropH = pBMI->biWidth - biRealWidth;
int cropV = pBMI->biHeight - biRealHeight;
if (cropH >= 0 && cropH <= 0x0f && cropV >= 0 && cropV <= 0x0f) {
m_pAVCtx->extradata = (uint8_t *)av_mallocz(1 + FF_INPUT_BUFFER_PADDING_SIZE);
m_pAVCtx->extradata_size = 1;
m_pAVCtx->extradata[0] = (cropH << 4) | cropV;
}
}
}

m_h264RandomAccess.flush(m_pAVCtx->thread_count);
m_CurrentThread = 0;
m_rtStartCache = AV_NOPTS_VALUE;

LAVPinInfo lavPinInfo = {0};
BOOL bLAVInfoValid = SUCCEEDED(m_pCallback->GetLAVPinInfo(lavPinInfo));

m_bInputPadded = dwDecFlags & LAV_VIDEO_DEC_FLAG_LAVSPLITTER;

// Setup codec-specific timing logic
BOOL bVC1IsPTS = (codec == AV_CODEC_ID_VC1 && !(dwDecFlags & LAV_VIDEO_DEC_FLAG_VC1_DTS));

// Use ffmpegs logic to reorder timestamps
// This is required for H264 content (except AVI), and generally all codecs that use frame threading
// VC-1 is also a special case. Its required for splitters that deliver PTS timestamps (see bVC1IsPTS above)
m_bFFReordering        =  ( codec == AV_CODEC_ID_H264 && !(dwDecFlags & LAV_VIDEO_DEC_FLAG_H264_AVI))
|| codec == AV_CODEC_ID_VP8
|| codec == AV_CODEC_ID_VP3
|| codec == AV_CODEC_ID_THEORA
|| codec == AV_CODEC_ID_HUFFYUV
|| codec == AV_CODEC_ID_FFVHUFF
|| codec == AV_CODEC_ID_MPEG2VIDEO
|| codec == AV_CODEC_ID_MPEG1VIDEO
|| codec == AV_CODEC_ID_DIRAC
|| codec == AV_CODEC_ID_UTVIDEO
|| codec == AV_CODEC_ID_DNXHD
|| codec == AV_CODEC_ID_JPEG2000
|| (codec == AV_CODEC_ID_MPEG4 && pmt->formattype == FORMAT_MPEG2Video)
|| bVC1IsPTS;

// Stop time is unreliable, drop it and calculate it
m_bCalculateStopTime   = (codec == AV_CODEC_ID_H264 || codec == AV_CODEC_ID_DIRAC || (codec == AV_CODEC_ID_MPEG4 && pmt->formattype == FORMAT_MPEG2Video) || bVC1IsPTS);

// Real Video content has some odd timestamps
// LAV Splitter does them allright with RV30/RV40, everything else screws them up
m_bRVDropBFrameTimings = (codec == AV_CODEC_ID_RV10 || codec == AV_CODEC_ID_RV20 || ((codec == AV_CODEC_ID_RV30 || codec == AV_CODEC_ID_RV40) && (!(dwDecFlags & LAV_VIDEO_DEC_FLAG_LAVSPLITTER) || (bLAVInfoValid && (lavPinInfo.flags & LAV_STREAM_FLAG_RV34_MKV)))));

// Enable B-Frame delay handling
m_bBFrameDelay = !m_bFFReordering && !m_bRVDropBFrameTimings;

m_bWaitingForKeyFrame = TRUE;
m_bResumeAtKeyFrame =    codec == AV_CODEC_ID_MPEG2VIDEO
|| codec == AV_CODEC_ID_VC1
|| codec == AV_CODEC_ID_RV30
|| codec == AV_CODEC_ID_RV40
|| codec == AV_CODEC_ID_VP3
|| codec == AV_CODEC_ID_THEORA
|| codec == AV_CODEC_ID_MPEG4;

m_bNoBufferConsumption =    codec == AV_CODEC_ID_MJPEGB
|| codec == AV_CODEC_ID_LOCO
|| codec == AV_CODEC_ID_JPEG2000;

m_bHasPalette = m_pAVCtx->bits_per_coded_sample <= 8 && m_pAVCtx->extradata_size && !(dwDecFlags & LAV_VIDEO_DEC_FLAG_LAVSPLITTER)
&&  (codec == AV_CODEC_ID_MSVIDEO1
|| codec == AV_CODEC_ID_MSRLE
|| codec == AV_CODEC_ID_CINEPAK
|| codec == AV_CODEC_ID_8BPS
|| codec == AV_CODEC_ID_QPEG
|| codec == AV_CODEC_ID_QTRLE
|| codec == AV_CODEC_ID_TSCC);

if (FAILED(AdditionaDecoderInit())) {
return E_FAIL;
}

if (bLAVInfoValid) {
// Setting has_b_frames to a proper value will ensure smoother decoding of H264
if (lavPinInfo.has_b_frames >= 0) {
DbgLog((LOG_TRACE, 10, L"-> Setting has_b_frames to %d", lavPinInfo.has_b_frames));
m_pAVCtx->has_b_frames = lavPinInfo.has_b_frames;
}
}

// Open the decoder
//打开解码器
int ret = avcodec_open2(m_pAVCtx, m_pAVCodec, NULL);
if (ret >= 0) {
DbgLog((LOG_TRACE, 10, L"-> ffmpeg codec opened successfully (ret: %d)", ret));
m_nCodecId = codec;
} else {
DbgLog((LOG_TRACE, 10, L"-> ffmpeg codec failed to open (ret: %d)", ret));
DestroyDecoder();
return VFW_E_UNSUPPORTED_VIDEO;
}

m_iInterlaced = 0;
for (int i = 0; i < countof(ff_interlace_capable); i++) {
if (codec == ff_interlace_capable[i]) {
m_iInterlaced = -1;
break;
}
}

// Detect chroma and interlaced
if (m_pAVCtx->extradata && m_pAVCtx->extradata_size) {
if (codec == AV_CODEC_ID_MPEG2VIDEO) {
CMPEG2HeaderParser mpeg2Parser(extra, extralen);
if (mpeg2Parser.hdr.valid) {
if (mpeg2Parser.hdr.chroma < 2) {
m_pAVCtx->pix_fmt = AV_PIX_FMT_YUV420P;
} else if (mpeg2Parser.hdr.chroma == 2) {
m_pAVCtx->pix_fmt = AV_PIX_FMT_YUV422P;
}
m_iInterlaced = mpeg2Parser.hdr.interlaced;
}
} else if (codec == AV_CODEC_ID_H264) {
CH264SequenceParser h264parser;
if (bH264avc)
h264parser.ParseNALs(extra+6, extralen-6, 2);
else
h264parser.ParseNALs(extra, extralen, 0);
if (h264parser.sps.valid)
m_iInterlaced = h264parser.sps.interlaced;
} else if (codec == AV_CODEC_ID_VC1) {
CVC1HeaderParser vc1parser(extra, extralen);
if (vc1parser.hdr.valid)
m_iInterlaced = (vc1parser.hdr.interlaced ? -1 : 0);
}
}

if (codec == AV_CODEC_ID_DNXHD)
m_pAVCtx->pix_fmt = AV_PIX_FMT_YUV422P10;
else if (codec == AV_CODEC_ID_FRAPS)
m_pAVCtx->pix_fmt = AV_PIX_FMT_BGR24;

if (bLAVInfoValid && codec != AV_CODEC_ID_FRAPS && m_pAVCtx->pix_fmt != AV_PIX_FMT_DXVA2_VLD)
m_pAVCtx->pix_fmt = lavPinInfo.pix_fmt;

DbgLog((LOG_TRACE, 10, L"AVCodec init successfull. interlaced: %d", m_iInterlaced));

return S_OK;
}

解码器销毁函数：DestroyDecoder()

//销毁解码器，各种Free
STDMETHODIMP CDecAvcodec::DestroyDecoder()
{
DbgLog((LOG_TRACE, 10, L"Shutting down ffmpeg..."));
m_pAVCodec	= NULL;

if (m_pParser) {
av_parser_close(m_pParser);
m_pParser = NULL;
}

if (m_pAVCtx) {
avcodec_close(m_pAVCtx);
av_freep(&m_pAVCtx->extradata);
av_freep(&m_pAVCtx);
}
av_frame_free(&m_pFrame);

av_freep(&m_pFFBuffer);
m_nFFBufferSize = 0;

av_freep(&m_pFFBuffer2);
m_nFFBufferSize2 = 0;

if (m_pSwsContext) {
sws_freeContext(m_pSwsContext);
m_pSwsContext = NULL;
}

m_nCodecId = AV_CODEC_ID_NONE;

return S_OK;
}