我需要一段能播放本地nv12文件的代码

您可以使用FFmpeg库来播放本地的nv12文件，以下是一个简单的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <math.h>
#include <unistd.h>
#include <fcntl.h>

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

#define INBUF_SIZE 4096

int main(int argc, char *argv[]) {
    AVFormatContext *pFormatCtx = NULL;
    AVCodecContext *pCodecCtx = NULL;
    AVCodec *pCodec = NULL;
    AVFrame *pFrame = NULL;
    AVPacket packet;
    int frameFinished;
    int videoStream;
    uint8_t *buffer;
    struct SwsContext *sws_ctx = NULL;
    int numBytes;
    int width, height;
    FILE *fp;
    char *filename = argv[1];

    // Open file
    fp = fopen(filename, "rb");
    if (!fp) {
        fprintf(stderr, "Failed to open file '%s'\n", filename);
        exit(1);
    }

    // Read file header
    if (fread(&width, sizeof(int), 1, fp) != 1 ||
        fread(&height, sizeof(int), 1, fp) != 1) {
        fprintf(stderr, "Failed to read file header\n");
        exit(1);
    }

    // Initialize FFmpeg
    av_register_all();
    avcodec_register_all();

    // Set up input format context
    pFormatCtx = avformat_alloc_context();
    if (!pFormatCtx) {
        fprintf(stderr, "Failed to allocate input format context\n");
        exit(1);
    }

    // Set up codec parameters
    pCodec = avcodec_find_decoder(AV_CODEC_ID_H264);
    if (!pCodec) {
        fprintf(stderr, "Failed to find decoder\n");
        exit(1);
    }
    pCodecCtx = avcodec_alloc_context3(pCodec);
    if (!pCodecCtx) {
        fprintf(stderr, "Failed to allocate codec context\n");
        exit(1);
    }
    pCodecCtx->width = width;
    pCodecCtx->height = height;
    pCodecCtx->pix_fmt = AV_PIX_FMT_NV12;

    // Open codec
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {
        fprintf(stderr, "Failed to open codec\n");
        exit(1);
    }

    // Allocate video frame
    pFrame = av_frame_alloc();
    if (!pFrame) {
        fprintf(stderr, "Failed to allocate frame\n");
        exit(1);
    }

    // Set up buffer for decoding
    numBytes = av_image_get_buffer_size(pCodecCtx->pix_fmt, pCodecCtx->width,
                                        pCodecCtx->height, 16);
    buffer = (uint8_t*) av_malloc(numBytes * sizeof(uint8_t));
    if (!buffer) {
        fprintf(stderr, "Failed to allocate buffer\n");
        exit(1);
    }
    av_image_fill_arrays(pFrame->data, pFrame->linesize, buffer,
                          pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, 16);

    // Read packets and decode frames
    while (1) {
        if (fread(packet.data, 1, INBUF_SIZE, fp) <= 0) {
            break;
        }
        packet.size = INBUF_SIZE;
        while (packet.size > 0) {
            int len = avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
            if (len < 0) {
                fprintf(stderr, "Error while decoding\n");
                exit(1);
            }
            if (frameFinished) {
                // Convert frame to RGB
                sws_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
                                         pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_RGB24,
                                         SWS_BILINEAR, NULL, NULL, NULL);
                if (!sws_ctx) {
                    fprintf(stderr, "Failed to get SwsContext\n");
                    exit(1);
                }
                sws_scale(sws_ctx, (uint8_t const * const *) pFrame->data, pFrame->linesize,
                          0, pCodecCtx->height, pFrame->data, pFrame->linesize);

                // Display frame
                // ...
            }
            packet.size -= len;
            packet.data += len;
        }
    }

    // Clean up
    fclose(fp);
    av_frame_free(&pFrame);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}

请注意：此代码仅演示了如何使用FFmpeg库播放本地的nv12文件，实际应用中需要根据具体情况进行修改。