用C语言调用ffmpeg的api读取文件的像素数据

以下是使用C语言调用FFmpeg的API读取文件的像素数据的示例代码：

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

#include <libavutil/imgutils.h>
#include <libavutil/parseutils.h>
#include <libavformat/avformat.h>

int main(int argc, char **argv)
{
    AVFormatContext *fmt_ctx = NULL;
    int video_stream_index = -1;
    AVCodecParameters *codec_params = NULL;
    AVCodec *decoder = NULL;
    AVCodecContext *decoder_ctx = NULL;
    AVFrame *frame = NULL;
    int ret, i;

    if (argc < 2) {
        fprintf(stderr, "Usage: %s <input_file>\n", argv[0]);
        return 1;
    }

    // Open input file
    ret = avformat_open_input(&fmt_ctx, argv[1], NULL, NULL);
    if (ret < 0) {
        fprintf(stderr, "Failed to open input file: %s\n", av_err2str(ret));
        goto end;
    }

    // Read stream information
    ret = avformat_find_stream_info(fmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Failed to read stream information: %s\n", av_err2str(ret));
        goto end;
    }

    // Find video stream
    for (i = 0; i < fmt_ctx->nb_streams; i++) {
        if (fmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_stream_index = i;
            break;
        }
    }
    if (video_stream_index == -1) {
        fprintf(stderr, "No video stream found in input file\n");
        goto end;
    }

    // Get codec parameters
    codec_params = fmt_ctx->streams[video_stream_index]->codecpar;

    // Find decoder
    decoder = avcodec_find_decoder(codec_params->codec_id);
    if (!decoder) {
        fprintf(stderr, "Failed to find decoder for codec ID %d\n", codec_params->codec_id);
        goto end;
    }

    // Allocate decoder context
    decoder_ctx = avcodec_alloc_context3(decoder);
    if (!decoder_ctx) {
        fprintf(stderr, "Failed to allocate decoder context\n");
        goto end;
    }

    // Copy codec parameters to decoder context
    ret = avcodec_parameters_to_context(decoder_ctx, codec_params);
    if (ret < 0) {
        fprintf(stderr, "Failed to copy codec parameters to decoder context: %s\n", av_err2str(ret));
        goto end;
    }

    // Open decoder
    ret = avcodec_open2(decoder_ctx, decoder, NULL);
    if (ret < 0) {
        fprintf(stderr, "Failed to open decoder: %s\n", av_err2str(ret));
        goto end;
    }

    // Allocate frame
    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Failed to allocate frame\n");
        goto end;
    }

    // Read frames from input file
    while (1) {
        AVPacket pkt = {0};
        av_init_packet(&pkt);

        ret = av_read_frame(fmt_ctx, &pkt);
        if (ret == AVERROR_EOF)
            break;
        if (ret < 0) {
            fprintf(stderr, "Failed to read frame: %s\n", av_err2str(ret));
            goto end;
        }

        // Decode packet
        ret = avcodec_send_packet(decoder_ctx, &pkt);
        if (ret < 0) {
            fprintf(stderr, "Failed to send packet to decoder: %s\n", av_err2str(ret));
            goto end;
        }

        while (ret >= 0) {
            ret = avcodec_receive_frame(decoder_ctx, frame);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                break;
            if (ret < 0) {
                fprintf(stderr, "Failed to receive frame from decoder: %s\n", av_err2str(ret));
                goto end;
            }

            // Process frame
            printf("Frame %d (type=%c, size=%d bytes) pts %d key_frame %d\n",
                   decoder_ctx->frame_number, av_get_picture_type_char(frame->pict_type),
                   frame->pkt_size, frame->pts, frame->key_frame);

            // Process pixel data
            uint8_t *data[AV_NUM_DATA_POINTERS] = {0};
            int linesize[AV_NUM_DATA_POINTERS] = {0};
            int width, height;

            data[0] = frame->data[0];
            linesize[0] = frame->linesize[0];
            width = frame->width;
            height = frame->height;

            // Process Y component
            for (i = 0; i < height; i++) {
                fwrite(data[0] + i * linesize[0], 1, width, stdout);
            }

            // Process U component
            if (codec_params->format == AV_PIX_FMT_YUV420P) {
                data[1] = frame->data[1];
                linesize[1] = frame->linesize[1];
                for (i = 0; i < height/2; i++) {
                    fwrite(data[1] + i * linesize[1], 1, width/2, stdout);
                }
            }

            // Process V component
            if (codec_params->format == AV_PIX_FMT_YUV420P) {
                data[2] = frame->data[2];
                linesize[2] = frame->linesize[2];
                for (i = 0; i < height/2; i++) {
                    fwrite(data[2] + i * linesize[2], 1, width/2, stdout);
                }
            }

            printf("\n");

            av_frame_unref(frame);
        }

        av_packet_unref(&pkt);
    }

end:
    if (frame)
        av_frame_free(&frame);
    if (decoder_ctx)
        avcodec_free_context(&decoder_ctx);
    if (fmt_ctx)
        avformat_close_input(&fmt_ctx);

    return ret;
}

此代码可读取输入文件中的视频帧，然后处理像素数据并将其写入stdout。在处理像素数据时，该代码将Y、U和V分量分别写入stdout。在处理像素数据时，还应注意缩放、旋转和其他处理，以使像素数据适合应用程序的需要。