本篇主要测试FFmpeg解码H264
代码逻辑：
-
1 寻找解码器 avcodec_find_decoder(AV_CODEC_ID_H264);
- 2 创建解码上下文 avcodec_alloc_context3(codec);
- 3 创建断帧上下文（对应编码的时候知道YUV一帧的数据量，解码的时候由于H264一帧多长并不知道，且没有规律，所以要先对读取的数据断帧）
av_parser_init(codec->id);
- 4 初始化解码上下文，打开解码器
由于解码的时候自然就得到视频参数，所以这里就不用额外设置参数了；编码的时候是需要设置GOP，FPS，W,H，level之类的
avcodec_open2(c, codec, NULL)
- 5 创建package装H264，创建frame装解码后的YUV
frame = av_frame_alloc();
pkt = av_packet_alloc();
- 6 开始断帧，送解码库解码（注意解码到最后一帧，要送一个空package，把解码库内部的缓存刷出来）
do {
/* read raw data from the input file */
data_size = fread(inbuf, 1, INBUF_SIZE, f);
if (ferror(f))
break;
eof = !data_size;
/* use the parser to split the data into frames */
data = inbuf;
while (data_size > 0 || eof) {
ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size,
data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
if (ret < 0) {
fprintf(stderr, "Error while parsing\n");
exit(1);
}
data += ret;
data_size -= ret;
if (pkt->size)
decode(c, frame, pkt, outfilename);
else if (eof)
break;
}
} while (!eof);
- 7 解码函数
avcodec_send_packet(dec_ctx, pkt);
解码输出：avcodec_receive_frame(dec_ctx, frame);
- 8 关闭上下文和文件
av_parser_close(parser); avcodec_free_context(&c); av_frame_free(&frame); av_packet_free(&pkt);
可运行代码：（注意YV12中YUV的存储顺序，和frame中数据所表达的意义）
代码中库的使用配置，可以参考我的上篇博客这里用的H264你可以从FFmpeg中用命令行提取一个，然后用下边的代码解码；我的这个264是处理问题时候其他组件保存的一个文件
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
extern "C" {
#include <libavcodec/avcodec.h>
char av_error[AV_ERROR_MAX_STRING_SIZE] = { 0 };
#define av_err2str(errnum) av_make_error_string(av_error, AV_ERROR_MAX_STRING_SIZE, errnum)
#define INBUF_SIZE 4096
static FILE* fout;
static void pgm_save(AVFrame*frame, int xsize, int ysize,
const char* filename)
{
int i;
if (!fout)
{
fout = fopen(filename, "wb");
}
//linesize中存储的是宽度，不是总长度
//写入顺序，Y V U =YV12 ;解码后的数据是YUV顺序存储的
for (i = 0; i < ysize; i++)
fwrite(frame->data[0] + i * frame->linesize[0], 1, xsize, fout);
for (i = 0; i < ysize/2; i++)
fwrite(frame->data[2] + i * frame->linesize[2], 1, xsize/2, fout);
for (i = 0; i < ysize / 2; i++)
fwrite(frame->data[1] + i * frame->linesize[1], 1, xsize/2, fout);
}
static void decode(AVCodecContext* dec_ctx, AVFrame* frame, AVPacket* pkt,
const char* filename)
{
char buf[1024];
int ret;
ret = avcodec_send_packet(dec_ctx, pkt);
if (ret < 0) {
fprintf(stderr, "Error sending a packet for decoding\n");
exit(1);
}
while (ret >= 0) {
ret = avcodec_receive_frame(dec_ctx, frame);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
return;
else if (ret < 0) {
fprintf(stderr, "Error during decoding\n");
exit(1);
}
printf("saving frame %3ld\n", dec_ctx->frame_num);
printf("YUV pts:%ld \n", frame->pts);
fflush(stdout);
/* the picture is allocated by the decoder. no need to
free it */
pgm_save(frame,frame->width, frame->height, filename);
}
}
int main(int argc, char** argv)
{
const char* filename, * outfilename;
const AVCodec* codec;
AVCodecParserContext* parser;
AVCodecContext* c = NULL;
FILE* f;
AVFrame* frame;
uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
uint8_t* data;
size_t data_size;
int ret;
int eof;
AVPacket* pkt;
//注意直接解码要从I帧开始，所以如果H264开头不是关键帧是要报错的
filename = "D:/Emscripten/cmaketest/catch.264";
outfilename = "D:/Emscripten/cmaketest/catch_out.yuv";
pkt = av_packet_alloc();
if (!pkt)
exit(1);
/* set end of buffer to 0 (this ensures that no overreading happens for damaged MPEG streams) */
memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
/* find the MPEG-1 video decoder */
codec = avcodec_find_decoder(AV_CODEC_ID_H264);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
//用来给H264断帧
parser = av_parser_init(codec->id);
if (!parser) {
fprintf(stderr, "parser not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c) {
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
/* For some codecs, such as msmpeg4 and mpeg4, width and height
MUST be initialized there because this information is not
available in the bitstream. */
/* open it */
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
f = fopen(filename, "rb");
if (!f) {
fprintf(stderr, "Could not open %s\n", filename);
exit(1);
}
frame = av_frame_alloc();
if (!frame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(1);
}
do {
/* read raw data from the input file */
data_size = fread(inbuf, 1, INBUF_SIZE, f);
if (ferror(f))
break;
eof = !data_size;
/* use the parser to split the data into frames */
data = inbuf;
while (data_size > 0 || eof) {
ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size,
data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
if (ret < 0) {
fprintf(stderr, "Error while parsing\n");
exit(1);
}
data += ret;
data_size -= ret;
if (pkt->size)
decode(c, frame, pkt, outfilename);
else if (eof)
break;
}
} while (!eof);
/* flush the decoder */
decode(c, frame, NULL, outfilename);
fclose(f);
av_parser_close(parser);
avcodec_free_context(&c);
av_frame_free(&frame);
av_packet_free(&pkt);
if (fout)
{
fclose(fout);
fout = nullptr;
}
return 0;
}
}
解码后的数据用elecard软件看，YUV正常，且颜色也是正常的：如果你看到颜色不对，可能是UV没放置好；
