ffmpeg как сохранить кадр в pgm

#include <iostream>
extern "C"
{
#include "libavcodec/avcodec.h"
 
#include "libavcodec/avfft.h"
 
#include "libavdevice/avdevice.h"
 
#include "libavfilter/avfilter.h"
 
#include "libavfilter/buffersink.h"
#include "libavfilter/buffersrc.h"
 
#include "libavformat/avformat.h"
#include "libavformat/avio.h"
 
    // libav resample
 
#include "libavutil/opt.h"
#include "libavutil/common.h"
#include "libavutil/channel_layout.h"
#include "libavutil/imgutils.h"
#include "libavutil/mathematics.h"
#include "libavutil/samplefmt.h"
#include "libavutil/time.h"
#include "libavutil/opt.h"
#include "libavutil/pixdesc.h"
#include "libavutil/file.h"
#include "libswscale/swscale.h"
 
// sdl2
 
}
 
#include <iostream>
#include <string>
static void save_gray_frame(unsigned char* buf, int wrap, int xsize, int ysize, char* filename)
{
    FILE* f;
    int i;
    f = fopen(filename, "wb");
    // writing the minimal required header for a pgm file format
    // portable graymap format -> https://en.wikipedia.org/wiki/Netpbm_format#PGM_example
    fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
 
    // writing line by line
    for (i = 0; i < ysize; i++)
        fwrite(buf + i * wrap, 1, xsize, f);
    fclose(f);
}
int main() {
    char buf[1024];
    AVFormatContext* pFormatContext = avformat_alloc_context();
    avformat_open_input(&pFormatContext, "rtsp://192.168.0.87:8080/h264_ulaw.sdp", NULL, NULL);
    avformat_find_stream_info(pFormatContext, NULL);
    AVCodecParameters* pLocalCodecParameters = 0;
 
    
    for (int i = 0; i < pFormatContext->nb_streams; i++) {
        pLocalCodecParameters = pFormatContext->streams[i]->codecpar;
    }
    av_read_play(pFormatContext);
    const AVCodec* pLocalCodec = avcodec_find_decoder(pLocalCodecParameters->codec_id);
    
    printf("%d", pLocalCodec);
 
    AVCodecContext* pCodecContext = avcodec_alloc_context3(pLocalCodec);
    avcodec_parameters_to_context(pCodecContext, pLocalCodecParameters);
    avcodec_open2(pCodecContext, pLocalCodec, NULL);
 
    AVPacket* pPacket = av_packet_alloc();
    AVFrame* pFrame = av_frame_alloc();
 
    for (int i = 0; i < 10;i++) {
        av_read_frame(pFormatContext, pPacket);
        avcodec_send_packet(pCodecContext, pPacket);
        avcodec_receive_frame(pCodecContext, pFrame);
        snprintf(buf, sizeof(buf), "%d-%s", pCodecContext->frame_number,"filename.pgm");
        save_gray_frame(pFrame->data[0], pFrame->linesize[0],
            pFrame->width, pFrame->height, buf);
        save_gray_frame(pFrame->data[0], pFrame->linesize[0], pFrame->width, pFrame->height, buf);
    }
    avformat_close_input(&pFormatContext);
}