Windows下ffmpeg调用测试——解码H264为YUV420P

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);

#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;
}

}