运用ffmpeg SDK解264码流(来源FFmpeg工程组)
Link：http://www.ffmpeg.com.cn/index.php/%E8%BF%90%E7%94%A8SDK%E8%A7%A3264%E7%A0%81%E6%B5%81运用SDK解264码流 方法一：最好参考ffmpeg自带的两个例子，outputexample.c和apiexample.c文件，亦或直接看ffmpeg和ffplay的例程也可，如果你是需要重量级的使用ffmpeg的话方法二（比较麻烦一点）：这是一个网上的例程http://www.inb.uni-luebeck.de/~boehme/avcodec_sample.cpp为方便全部贴出如下：#include "avcodec.h"
#include "avformat.h"
#include <stdlib.h>
#include <time.h>
#include <stdio.h>
/* new types */
enum bool{false=0,true};
typedef enum bool bool;
static bool GetNextFrame(AVFormatContext *pFormatCtx, AVCodecContext *pCodecCtx,int videoStream, AVFrame *pFrame)
{
static AVPacket packet;
static int bytesRemaining=0;
static uint8_t*rawData;
static bool fFirstTime=true;
int bytesDecoded;
int frameFinished;
// First time we're called, set packet.data to NULL to indicate it
// doesn't have to be freed
if (fFirstTime){
fFirstTime = false;
packet.data = NULL;
}
// Decode packets until we have decoded a complete frame
while (true)
{
// Work on the current packet until we have decoded all of it
while (bytesRemaining > 0)
{
// Decode the next chunk of data
bytesDecoded = avcodec_decode_video(pCodecCtx, pFrame,
&frameFinished, rawData, bytesRemaining);
// Was there an error?
if (bytesDecoded < 0){
fprintf(stderr, "Error while decoding frame\n");
return false;
}
bytesRemaining -= bytesDecoded;
rawData += bytesDecoded;
// Did we finish the current frame? Then we can return
if (frameFinished)
return true;
}
// Read the next packet, skipping all packets that aren't for this
// stream
do{
// Free old packet
if(packet.data != NULL)
av_free_packet(&packet);
// Read new packet
if(av_read_packet(pFormatCtx, &packet) < 0)
goto loop_exit;
} while(packet.stream_index != videoStream);
bytesRemaining = packet.size;
rawData = packet.data;
}
loop_exit:
// Decode the rest of the last frame
bytesDecoded = avcodec_decode_video(pCodecCtx, pFrame, &frameFinished,
rawData, bytesRemaining);
// Free last packet
if(packet.data != NULL)
av_free_packet(&packet);
return frameFinished != 0;
}
int main()
{
AVFormatContext *pFormatCtx;
int i, videoStream;
AVCodecContext*pCodecCtx;
AVCodec *pCodec;
AVFrame *pFrame;
AVFrame *pFrameYUV;
clock_t t;
double fps;
int y_size, i_frame=0;
int numBytes;
uint8_t *buffer;
char* infile="test.264";
char* outfile="out.yuv";
FILE* fp=fopen(outfile, "wb");
if (fp==NULL){
fprintf(stderr, "\nCan't open file %s!", infile);
return -1;
}
// Register all formats and codecs
av_register_all();
// Open video file
if (av_open_input_file(&pFormatCtx, infile, NULL, 0, NULL) != 0)
return -1; // Couldn't open file
// Retrieve stream information
if (av_find_stream_info(pFormatCtx) < 0)
return -1; // Couldn't find stream information
// Dump information about file onto standard error
dump_format(pFormatCtx, 0, infile, false);
t = clock();
// Find the first video stream
videoStream = -1;
for (i=0; i<pFormatCtx->nb_streams; i++)
if(pFormatCtx->streams[/*此处不隔开，后面的字体全部是斜体*/i]->codec->codec_type == CODEC_TYPE_VIDEO){
videoStream=i;
break;
}
if (videoStream == -1)
return -1; // Didn't find a video stream
// Get a pointer to the codec context for the video stream
pCodecCtx = pFormatCtx->streams->codec;
// Find the decoder for the video stream
pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
if (pCodec == NULL)
return -1; // Codec not found
// Inform the codec that we can handle truncated bitstreams -- i.e.,
// bitstreams where frame boundaries can fall in the middle of packets
if(pCodec->capabilities & CODEC_CAP_TRUNCATED)
pCodecCtx->flags|=CODEC_FLAG_TRUNCATED;
// Open codec
if (avcodec_open(pCodecCtx, pCodec) < 0)
return -1; // Could not open codec
// Allocate video frame
pFrame = avcodec_alloc_frame();
// Allocate an AVFrame structure
pFrameYUV=avcodec_alloc_frame();
if(pFrameYUV == NULL)
return -1;
// Determine required buffer size and allocate buffer
numBytes=avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width,
pCodecCtx->height);
buffer = (uint8_t*)malloc(numBytes);
// Assign appropriate parts of buffer to image planes in pFrameRGB
avpicture_fill((AVPicture *)pFrameYUV, buffer, PIX_FMT_YUV420P,
pCodecCtx->width, pCodecCtx->height);
// Read frames
while(GetNextFrame(pFormatCtx, pCodecCtx, videoStream, pFrame))
{
img_convert((AVPicture *)pFrameYUV, PIX_FMT_YUV420P, (AVPicture*)pFrame,
pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
i_frame++;
y_size = pCodecCtx->width * pCodecCtx->height;
#if 1
if (i_frame==1) //only output onr time
{
printf("\n:lolpFrame->linesize=%d, pFrame->linesize=%d, pFrame->linesize=%d!\n",
pFrame->linesize[0], pFrame->linesize[1], pFrame->linesize[2]);
printf("\n:lolpFrameYUV->linesize=%d, pFrameYUV->linesize=%d, pFrameYUV->linesize=%d!",
pFrameYUV->linesize[0], pFrameYUV->linesize[1], pFrameYUV->linesize[2]);
}
#endif
fwrite(pFrameYUV->data[0], 1, y_size, fp);
fwrite(pFrameYUV->data[1], 1, (y_size/4), fp);
fwrite(pFrameYUV->data[2], 1, (y_size/4), fp);
}
//calculate decode rate
fclose(fp);
t = clock() - t;
fps = (double)(t) / CLOCKS_PER_SEC;
fps = i_frame / fps;
printf("\n==>Decode rate %.4f fps!\n", fps);
// Free the YUV image
free(buffer);
av_free(pFrameYUV);
// Free the YUV frame
av_free(pFrame);
// Close the codec
avcodec_close(pCodecCtx);
// Close the video file
av_close_input_file(pFormatCtx);
return 0;
}复制代码
将以上例程作如下修改： 1.将GetNextFrame里面的函数av_read_packet改成av_read_frame； 2.解码后一帧YUV的保存，可以按fastreaming的方法（具体方法如下），另外重新定义一YUV420P格式，调用img_convert 将解码后的帧转换到新定义的帧里面去。后者可能稍微耗时一些，但这样接口更清晰一些，便于封装，可直接用于显示等。 3.该程序对解码后的最后一帧，需在循环体while后面，才能再次写解码帧的数据。否则你将会看到解码少1帧。可以参考apiexample里面。 4.如果要使用以下这一段的话 if(g_ffmpeg_pCodec->capabilities&CODEC_CAP_TRUNCATED) g_ffmpeg_pCodecCtx->flags|= CODEC_FLAG_TRUNCATED; 这一段在使用av_read_frame的时候是一定要去掉的，否则严重丢失数据。我用av_read_frame的时候没有去掉那两句。结果380多桢的一个视频文件只 解出190多桢。而且中间有很多桢都是花的。类似劣质VCD被卡的那种画面。去掉以后一切OK。
fastreaming的方法source :352x288
internal: (16+352+16) x288
FFmpeg adds 16 pixels at four edges of a frame just for enhancing MC/ME
result:
you get:
linesize[0] = (16+352+16) = 384
linesize[1] = linesize[0]/2;
linesize[2] = linesize[0]/2
but data[0],data[1],data[2] is just the address of valid YUV pixels, but the valid data length is 352,176,176 separately
Now I think you can figure out the layout of a YUV frame which is generated by FFmpeg decoder
Please ref the following function to dump yuv data
int g_yuv_index = 1;
void smartAV_dump_yuv(char *file_name,AVPicture *pic,int width,int height)
{
FILE *fp =0;
char filename[128],index_name[32];
int i,j,shift;
uint8_t *yuv_factor;
strcpy(filename,file_name);
sprintf(index_name,"new_yuv_dump_%d.yuv",g_yuv_index);
strcat(filename,index_name);
fp = fopen(filename,"wb");
if(fp) {
for(i = 0; i < 3; i++) {
shift = (i == 0 ? 0:1);
yuv_factor = pic->data;
for(j = 0; j < (height>>shift); j++) {
fwrite(yuv_factor,(width>>shift),1,fp);
yuv_factor += pic->linesize;
}
}
fclose(fp);
g_yuv_index++;
}
}
ource :352x288
internal: (16+352+16) x(16+288+16)
FFmpeg adds 16 pixels at four edges of a frame just for enhancing MC/ME
result:
you get:
linesize[0] = (16+352+16) = 384
linesize[1] = linesize[0]/2;
linesize[2] = linesize[0]/2
but data[0],data[1],data[2] is just the address of valid YUV pixels, but the valid data length is 352,176,176 per line
separately
and there is 288 lines valid for data[0], data[1]: 144,data[2] :144
Now I think you can figure out the layout of a YUV frame which is generated by FFmpeg decoder
Please ref the following function to dump yuv data
int g_yuv_index = 1;
void smartAV_dump_yuv(char *file_name,AVPicture *pic,int width,int height)
{
FILE *fp =0;
char filename[128],index_name[32];
int i,j,shift;
uint8_t *yuv_factor;
strcpy(filename,file_name);
sprintf(index_name,"new_yuv_dump_%d.yuv",g_yuv_index);
strcat(filename,index_name);
fp = fopen(filename,"wb");
if(fp) {
for(i = 0; i < 3; i++) {
shift = (i == 0 ? 0:1);
yuv_factor = pic->data;
for(j = 0; j < (height>>shift); j++) {
fwrite(yuv_factor,(width>>shift),1,fp);
yuv_factor += pic->linesize;
}
}
fclose(fp);
g_yuv_index++;
}
}复制代码
有关该问题的讨论帖可参考ffmpeg工程组论坛中的相关讨论：有关运用SDK解264码流的讨论
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