ffmpeg實時解碼H264數據流

以下是一個測試程序，用的是讀取h264文件數據然後用ffmpeg解碼的方法，模擬實時數據的解碼。測試已通過，解碼正常。

至於如何編譯ffmpeg、如何實現收發數據、如何拼幀這裏不予說明，請查看相關文檔。
 
 1、.h文件裏面

#ifdef __cplusplus

extern "C" {

#endif

#include "libavformat/avformat.h"

#include "libavutil/opt.h"

#include "libavutil/imgutils.h"

#include "libavcodec/avcodec.h"

#include "libswscale/swscale.h"

#pragma comment(lib, "libgcc.a")

#pragma comment(lib, "libavcodec.a")

#pragma comment(lib, "libavformat.a")

#pragma comment(lib, "libavutil.a")

#pragma comment(lib, "libmingwex.a")

#ifdef __cplusplus

}

#endif 


2、.cpp文件裏面

//寫YUV（420P）數據
 FILE *g_fd_yuv420p = fopen("C:\\decodeTest\\420p_stream.yuv", "wb");

static void SaveFrame_YUV420P_2(AVFrame *pFrame, int width, int height, int iFrame){

if(g_fd_yuv420p != NULL){

if(pFrame != NULL){

unsigned int pos = 0;

for(int y=0; y<height; y++){

fwrite(pFrame->data[0] + y * pFrame->linesize[0], 1, width, g_fd_yuv420p);

}

for(int y=0; y<(height / 2); y++){

fwrite(pFrame->data[1] + y * pFrame->linesize[1], 1, width / 2, g_fd_yuv420p);

}

for(int y=0; y<(height / 2); y++){

fwrite(pFrame->data[2] + y * pFrame->linesize[2], 1, width / 2, g_fd_yuv420p);

}

}else{

fclose(g_fd_yuv420p);

}

}

}

//獲取H264數據流中下一個幀開始的位置

int getNextNalPos(unsigned char *pData, int startPos, int dataLength, unsigned long *pPos){

if(pData != NULL && startPos >= 0 && (dataLength - startPos) > 4){

unsigned char *pTmp = pData + startPos;

int restLen = dataLength - startPos;

while(restLen >= 5){

int *p = (int *)pTmp;

if(p[0] == 0x01000000){

*pPos = (pTmp - pData);

if(pTmp[4] == 0x67){

return 1;//SPS

}else if(pTmp[4] == 0x68){

return 2;//PPS

}else{

return 0;

}

}

restLen --;

pTmp ++;

}

}

return -1;

}

//測試函數

void CtestCodecDlg::OnBnClickedButton2()

{

AVCodec *pCodec = NULL;

AVCodecContext *pContext = NULL;

AVFrame *pFrame = NULL;

AVPacket packet = {0};

av_register_all();

pCodec = avcodec_find_decoder(CODEC_ID_H264);

if(pCodec == NULL){

LOG("沒有找到H264 codec");

goto stream_decode_finish;

}

pContext = avcodec_alloc_context3(pCodec);

if(pContext == NULL){

LOG("avcodec_alloc_context3 失敗");

goto stream_decode_finish;

}

pContext->time_base.num = 1;

pContext->time_base.den = 25;

pContext->bit_rate = 0;

pContext->frame_number = 1;

pContext->codec_type = AVMEDIA_TYPE_VIDEO;
        //圖像寬高的求解看第三步 

pContext->width = 352;

pContext->height = 288;

/* pContext->pix_fmt = AV_PIX_FMT_YUV420P;

pContext->profile = 578;

pContext->level = 13;

pContext->pkt_timebase.num = 1;

pContext->pkt_timebase.den = 1200000;*/

if(avcodec_open2(pContext, pCodec, NULL) < 0){

LOG("avcodec_open2 失敗");

goto stream_decode_finish;

}

pFrame = avcodec_alloc_frame();

if(pFrame == NULL){

LOG("avcodec_alloc_frame 失敗");

goto stream_decode_finish;

}

unsigned long cacheSize = (1024 << 10);

unsigned char *pSrcData = (unsigned char *)malloc(cacheSize);

if(pSrcData == NULL){

LOG("malloc 失敗");

goto stream_decode_finish;

}

memset(pSrcData, 0, cacheSize);

FILE *fd = fopen("C:\\out_2.h264", "rb");

// FILE *fd = fopen("C:\\gaoqing.h264", "rb");

if(fd == NULL){

LOG("fopen 失敗");

goto stream_decode_finish;

}

/* unsigned char extraData[64] = {0};

fread(extraData, 1, 36, fd);

pContext->extradata = extraData;

pContext->extradata_size = 36;

fseek(fd, 0, SEEK_SET);*/

int fdPos = 0;//文件指針

int frameNum = 1;

while(true){

bool bBreak = false;

int readLen = fread(pSrcData, 1, cacheSize, fd);

if(readLen < cacheSize){

fseek(fd, 0, SEEK_SET);

bBreak = true;

}

int pos = 0;

int processedLen = 0;

unsigned long nextNalPos = 0;

int ret = getNextNalPos(pSrcData, processedLen, readLen, &nextNalPos);

int nalType = -1;

while(ret != -1){

//TRACE("nextPos: %0x\n", nextNalPos);

if(ret == 1){

int tmpLen = nextNalPos - pos;

if(tmpLen > 0){//解碼

packet.data = pSrcData + pos;

packet.size = tmpLen;

fdPos += tmpLen;

int frameFinished = 0;

int result = avcodec_decode_video2(pContext, pFrame, &frameFinished, &packet);

if(ret < 0){

LOG("avcodec_decode_video2 failed");

}

if(frameFinished){

// TRACE("frameNum: %d, processedLen: %d\n", frameNum ++, processedLen);

SaveFrame_YUV420P_2(pFrame, pContext->width, pContext->height, 0);

}

pos = nextNalPos;

}

processedLen = nextNalPos + 5;

nalType = 1;

}else if(ret == 2){

if(nalType == 0){

packet.data = pSrcData + pos;

packet.size = nextNalPos - pos;

fdPos += packet.size;

int frameFinished = 0;

int result = avcodec_decode_video2(pContext, pFrame, &frameFinished, &packet);

if(ret < 0){

LOG("avcodec_decode_video2 failed");

}

if(frameFinished){

// TRACE("frameNum: %d, processedLen: %d\n", frameNum ++, processedLen);

SaveFrame_YUV420P_2(pFrame, pContext->width, pContext->height, 0);

}

pos = nextNalPos;

}

processedLen = nextNalPos + 5;

nalType = 2;

}else if(ret == 0){

{

packet.data = pSrcData + pos;

packet.size = nextNalPos - pos;

fdPos += packet.size;

int frameFinished = 0;

int result = avcodec_decode_video2(pContext, pFrame, &frameFinished, &packet);

if(ret < 0){

LOG("avcodec_decode_video2 failed");

}

if(frameFinished){

// TRACE("frameNum: %d, processedLen: %d\n", frameNum ++, processedLen);

SaveFrame_YUV420P_2(pFrame, pContext->width, pContext->height, 0);

}

pos = nextNalPos;

}

processedLen = nextNalPos + 5;

nalType = 0;

}

ret = getNextNalPos(pSrcData, processedLen, readLen, &nextNalPos);

}

//TRACE("重新讀取緩存！！位置：%d，processedLength：%d\n", fdPos, processedLen);

fseek(fd, fdPos, SEEK_SET);

if(bBreak){

break;

}

}

SaveFrame_YUV420P_2(pFrame, pContext->width, pContext->height, 0);

stream_decode_finish:

if(pFrame != NULL){

av_freep(&pFrame);

avcodec_free_frame(&pFrame);

}

if(pContext != NULL){

avcodec_close(pContext);

av_free(pContext);

}

if(pSrcData != NULL){

free(pSrcData);

pSrcData = NULL;

}

if(fd != NULL){

fclose(fd);

fd = NULL;

}

return;

}

3、相關說明
圖像的寬高可以從H264碼流的SPS中獲取，獲取方法：
SPS結構裏面有兩個數據成員：pic_width_in_mbs_minus1，pic_height_in_map_units_minus_1，分別表示圖像的寬和高，以宏塊（16x16）的值減1爲單位，因此圖像的實際寬爲（（pic_width_in_mbs_minus1 + 1）<< 4），實際高爲（（pic_height_in_map_units_minus_1  + 1）<< 4）。