c语言函数实现h264帧转yuv帧

实现 H264 帧转 YUV 帧的过程，可以分为如下几个步骤：

1. 读取 H264 数据，将其解码成原始的 YUV 数据。

2. 将 YUV 数据存储到文件中。

下面是一个示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <stdbool.h>

#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>

#define INBUF_SIZE 4096

int main(int argc, char *argv[]) {
    AVFormatContext *pFormatCtx = NULL;
    AVCodecContext *pCodecCtx = NULL;
    AVCodec *pCodec = NULL;
    AVPacket packet;
    AVFrame *pFrame = NULL;
    AVFrame *pFrameYUV = NULL;
    uint8_t *buffer = NULL;
    int videoStream = -1;
    int frameFinished = 0;
    int numBytes = 0;
    struct SwsContext *img_convert_ctx = NULL;

    if (argc < 3) {
        printf("Usage: %s <input_file> <output_file>\n", argv[0]);
        return -1;
    }

    av_register_all();

    if (avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) != 0) {
        printf("Error: Couldn't open input file.\n");
        return -1;
    }

    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        printf("Error: Couldn't find stream information.\n");
        return -1;
    }

    for (int i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoStream = i;
            break;
        }
    }

    if (videoStream == -1) {
        printf("Error: Couldn't find video stream.\n");
        return -1;
    }

    pCodecCtx = avcodec_alloc_context3(NULL);
    if (!pCodecCtx) {
        printf("Error: Couldn't allocate codec context.\n");
        return -1;
    }

    avcodec_parameters_to_context(pCodecCtx, pFormatCtx->streams[videoStream]->codecpar);

    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == NULL) {
        printf("Error: Couldn't find codec.\n");
        return -1;
    }

    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {
        printf("Error: Couldn't open codec.\n");
        return -1;
    }

    pFrame = av_frame_alloc();
    pFrameYUV = av_frame_alloc();
    if (!pFrame || !pFrameYUV) {
        printf("Error: Couldn't allocate frames.\n");
        return -1;
    }

    numBytes = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height, 1);
    buffer = (uint8_t *)av_malloc(numBytes * sizeof(uint8_t));
    if (!buffer) {
        printf("Error: Couldn't allocate buffer.\n");
        return -1;
    }

    av_image_fill_arrays(pFrameYUV->data, pFrameYUV->linesize, buffer, AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height, 1);

    img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, 0, NULL, NULL, NULL);
    if (!img_convert_ctx) {
        printf("Error: Couldn't initialize conversion context.\n");
        return -1;
    }

    FILE *fp_out = fopen(argv[2], "wb");
    if (!fp_out) {
        printf("Error: Couldn't open output file.\n");
        return -1;
    }

    while (av_read_frame(pFormatCtx, &packet) >= 0) {
        if (packet.stream_index == videoStream) {
            avcodec_send_packet(pCodecCtx, &packet);
            while (avcodec_receive_frame(pCodecCtx, pFrame) == 0) {
                sws_scale(img_convert_ctx, (const uint8_t *const *)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);
                fwrite(pFrameYUV->data[0], 1, pCodecCtx->width * pCodecCtx->height, fp_out);
                fwrite(pFrameYUV->data[1], 1, pCodecCtx->width * pCodecCtx->height / 4, fp_out);
                fwrite(pFrameYUV->data[2], 1, pCodecCtx->width * pCodecCtx->height / 4, fp_out);
            }
            av_packet_unref(&packet);
        }
    }

    fclose(fp_out);

    av_free(buffer);
    av_frame_free(&pFrameYUV);
    av_frame_free(&pFrame);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}

其中，`AVFormatContext` 用于存储输入文件的格式信息，`AVCodecContext` 用于存储编解码器的上下文信息，`AVCodec` 用于存储编解码器的信息，`AVPacket` 用于存储解码后的数据帧，`AVFrame` 用于存储解码后的数据帧，`SwsContext` 用于存储图像转换上下文信息。