从设备采集mjpeg格式的流，转成h264的数据

将MJPEG格式的流转换为H.264格式的数据，可以借助FFmpeg这个开源的多媒体处理库来实现。下面是一个简单的示例代码，可以实现将MJPEG流转换为H.264流的功能：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libavutil/imgutils.h>
#include <libavutil/opt.h>
#include <libavutil/parseutils.h>
#include <libavutil/pixdesc.h>
#include <libavcodec/avcodec.h>

#define INBUF_SIZE 4096

int main(int argc, char **argv)
{
    AVCodec *codec;
    AVCodecContext *c = NULL;
    int ret;
    AVFrame *frame;
    AVPacket *pkt;
    uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
    uint8_t *data;
    size_t   data_size;
    FILE *f;
    int i;

    if (argc <= 2) {
        fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
        exit(0);
    }

    avcodec_register_all();

    codec = avcodec_find_encoder(AV_CODEC_ID_H264);
    if (!codec) {
        fprintf(stderr, "Codec not found\n");
        exit(1);
    }

    c = avcodec_alloc_context3(codec);
    if (!c) {
        fprintf(stderr, "Could not allocate video codec context\n");
        exit(1);
    }

    /* Set the codec context properties */
    c->bit_rate = 400000;
    c->width    = 352;
    c->height   = 288;

    /* Set the frame rate */
    AVRational framerate = {25,1};
    c->time_base = framerate;
    c->framerate = framerate;

    c->gop_size      = 10;
    c->max_b_frames  = 1;
    c->pix_fmt       = AV_PIX_FMT_YUV420P;

    if (avcodec_open2(c, codec, NULL) < 0) {
        fprintf(stderr, "Could not open codec\n");
        exit(1);
    }

    /* Allocate the input buffer */
    pkt = av_packet_alloc();
    if (!pkt) {
        fprintf(stderr, "Could not allocate packet\n");
        exit(1);
    }

    /* Open the input file */
    f = fopen(argv[1], "rb");
    if (!f) {
        fprintf(stderr, "Could not open %s\n", argv[1]);
        exit(1);
    }

    /* Open the output file */
    FILE *outfile = fopen(argv[2], "wb");
    if (!outfile) {
        fprintf(stderr, "Could not open %s\n", argv[2]);
        exit(1);
    }

    /* Allocate the frame */
    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Could not allocate video frame\n");
        exit(1);
    }

    /* Fill the input buffer */
    data_size = fread(inbuf, 1, INBUF_SIZE, f);
    data      = inbuf;

    while (data_size > 0) {
        /* Set the input buffer properties */
        AVFrame *frame = av_frame_alloc();
        if (!frame) {
            fprintf(stderr, "Could not allocate video frame\n");
            exit(1);
        }
        frame->width = c->width;
        frame->height = c->height;
        frame->format = c->pix_fmt;

        int ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height, c->pix_fmt, 32);
        if (ret < 0) {
            fprintf(stderr, "Could not allocate raw picture buffer\n");
            exit(1);
        }

        /* Fill the frame with the input buffer data */
        av_image_fill_arrays(frame->data, frame->linesize, data, c->pix_fmt, c->width, c->height, 32);

        /* Encode the frame */
        ret = avcodec_send_frame(c, frame);
        if (ret < 0) {
            fprintf(stderr, "Error sending a frame for encoding\n");
            exit(1);
        }

        while (ret >= 0) {
            ret = avcodec_receive_packet(c, pkt);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                break;
            } else if (ret < 0) {
                fprintf(stderr, "Error during encoding\n");
                exit(1);
            }

            fwrite(pkt->data, 1, pkt->size, outfile);
            av_packet_unref(pkt);
        }

        data += data_size;
        data_size = fread(inbuf, 1, INBUF_SIZE, f);
    }

    /* Flush the encoder */
    ret = avcodec_send_frame(c, NULL);
    if (ret < 0) {
        fprintf(stderr, "Error flushing the encoder\n");
        exit(1);
    }

    while (ret >= 0) {
        ret = avcodec_receive_packet(c, pkt);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
            break;
        } else if (ret < 0) {
            fprintf(stderr, "Error during encoding\n");
            exit(1);
        }

        fwrite(pkt->data, 1, pkt->size, outfile);
        av_packet_unref(pkt);
    }

    /* Free resources */
    fclose(f);
    fclose(outfile);
    avcodec_free_context(&c);
    av_frame_free(&frame);
    av_packet_free(&pkt);

    return 0;
}

请注意，这个示例代码只是一个简单的转换过程，可能需要根据实际情况进行修改和优化。同时，这个示例代码也不能处理所有的MJPEG流，需要根据实际情况进行调整。