ffmpeg 解码视频（h264、mpeg2）输出yuv420p文件
播放yuv可以参考：ffplay -pixel_format yuv420p -video_size 768x320 -framerate 25 out.yuv
main.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libavutil/frame.h>
#include <libavutil/mem.h>
#include <libavcodec/avcodec.h>
#define VIDEO_INBUF_SIZE 10240
#define VIDEO_REFILL_THRESH 4096
static void decode(AVCodecContext* dec_ctx, AVPacket* pkt, AVFrame* frame, FILE* outfile)
{
int ret;
//发一帧数据进行解码
int send_ret = 1;
do
{
ret = avcodec_send_packet(dec_ctx, pkt);
if(ret == AVERROR(EAGAIN))//AVERROR(EAGAIN) 传入失败，表示先要receive frame再重新send packet
{
send_ret = 0;
printf("avcodec_send_packet ret == AVERROR(EAGAIN)\n");
}
else if(ret < 0)
{
printf("avcodec_send_packet ret < 0\n");
return;
}
while(ret >= 0)
{
//调用avcodec_receive_frame会在内部首先调用av_frame_unref来释放frame本来的数据
//就是这次调用会将上次调用返回的frame数据释放
ret = avcodec_receive_frame(dec_ctx, frame);
if(ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
return;
else if(ret < 0)
{
printf("avcodec_receive_frame = ret < 0\n");
return;
}
//在第一帧的时候输出一下音频信息
static int print_info = 1;
if(print_info)
{
print_info = 0;
printf("width : %uHz\n", frame->width);
printf("height : %u\n", frame->height);
printf("fformat : %u\n", frame->format);
}
//写入h264文件，yuv420p
//yuv420格式 ：yyyyyyy......uuuu.....vvvvv.......
fwrite(frame->data[0], 1, frame->width * frame->height, outfile);//y分量
fwrite(frame->data[1], 1, (frame->width) * (frame->height) / 4, outfile);//u分量
fwrite(frame->data[2], 1, (frame->width) * (frame->height) / 4, outfile);//v分量
}
}while(!send_ret);
}
#define H264 0
int main()
{
printf("Hello video decoder!\n");
const char* outfilename = "out.yuv";
#if H264
const char* filename = "test.h264";
#else
const char* filename = "test.mpeg2";
#endif
const AVCodec* codec = NULL;
AVCodecContext* codec_ctx = NULL;
AVCodecParserContext* parser = NULL;
int len = 0;
int ret = 0;
FILE* infile = NULL;
FILE* outfile = NULL;
// AV_INPUT_BUFFER_PADDING_SIZE 在输入比特流结尾的要求附加分配字节的数量上进行解码
//具体什么影响不知道
uint8_t inbuf[VIDEO_INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
uint8_t* data = NULL;
size_t data_size = 0;
AVPacket* pkt = NULL;
AVFrame* de_frame = NULL;
//申请AVPacket本身的内存
pkt = av_packet_alloc();
enum AVCodecID video_codec_id = AV_CODEC_ID_NONE;
if(strstr(filename, ".h264") != NULL)
{
video_codec_id = AV_CODEC_ID_H264;
}
else if(strstr(filename, ".mpeg2") != NULL)
{
video_codec_id = AV_CODEC_ID_MPEG2VIDEO;
}
else
{
printf("video_codec_id = AV_CODEC_ID_NONE\n");
return 0;
}
//查找解码器
codec = avcodec_find_decoder(video_codec_id);
if(!codec)
{
printf("Codec not find!\n");
return 0;
}
//根据解码器ID获取裸流的解析器
printf("video decoder end!\n");
parser = av_parser_init(codec->id);
if(!parser)
{
printf("Parser not find!\n");
return 0;
}
//分配codec使用的上下文
codec_ctx = avcodec_alloc_context3(codec);
if(!codec_ctx)
{
printf("avcodec_alloc_context3 failed!\n");
return 0;
}
//将解码器和解码使用的上下文关联
if(avcodec_open2(codec_ctx, codec, NULL) < 0)
{
printf("avcodec_open2 failed!\n");
return 0;
}
//打开文件
infile = fopen(filename, "rb");
if(!infile)
{
printf("infile fopen failed!\n");
return 0;
}
//输出文件
outfile = fopen(outfilename, "wb");
if(!outfile)
{
printf("outfilie fopen failed!\n");
return 0;
}
int file_end = 0;
//读取文件 开始解码
data = inbuf;
data_size = fread(inbuf, 1, VIDEO_INBUF_SIZE, infile);
de_frame = av_frame_alloc();
while (data_size > 0)
{
//获取传入到avcodec_send_packet一个packet的数据量
//(一帧)
ret = av_parser_parse2(parser, codec_ctx, &pkt->data, &pkt->size,
data, data_size,
AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
if(ret < 0)
{
printf("av_parser_parser2 Error!\n");
return 0;
}
//使用了多少数据做一个偏移
data += ret;
data_size -= ret;
if(pkt->size)
decode(codec_ctx, pkt, de_frame, outfile);
//如果当前缓冲区中数据少于VIDEO_REFILL_THRESH就再读
//避免多次读文件
if((data_size < VIDEO_REFILL_THRESH) && !file_end)
{
//剩余数据移动缓冲区前
memmove(inbuf, data, data_size);
data = inbuf;
//跨过已有数据存储
len = fread(data + data_size, 1, VIDEO_INBUF_SIZE - data_size, infile);
if(len > 0)
data_size += len;
else if(len == 0)
{
file_end = 1;
printf("file end!\n");
}
}
}
//冲刷解码器
pkt->data = NULL;
pkt->size = 0;
decode(codec_ctx, pkt, de_frame, outfile);
fclose(infile);
fclose(outfile);
avcodec_free_context(&codec_ctx);
av_parser_close(parser);
av_frame_free(&de_frame);
av_packet_free(&pkt);
printf("video decoder end!\n");
return 0;
}