如何在avformat_open_input()函数中设置编解码器？

#include <stdio.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>

int main() {
    AVFormatContext *formatContext = NULL;
    AVCodecContext *codecContext = NULL;
    AVCodec *codec = NULL;
    int streamIndex = -1;

    av_register_all();

    // Step 1: Open input file
    if (avformat_open_input(&formatContext, "input.mp4", NULL, NULL) != 0) {
        printf("Could not open input file\n");
        return -1;
    }

    // Step 2: Retrieve stream information
    if (avformat_find_stream_info(formatContext, NULL) < 0) {
        printf("Could not find stream information\n");
        return -1;
    }

    // Step 3: Find the audio/video stream
    for (int i = 0; i < formatContext->nb_streams; i++) {
        if (formatContext->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            streamIndex = i;
            break;
        }
    }

    if (streamIndex == -1) {
        printf("Could not find video stream\n");
        return -1;
    }

    // Step 4: Get the codec parameters
    AVStream *stream = formatContext->streams[streamIndex];
    AVCodecParameters *codecParams = stream->codecpar;

    // Step 5: Find the decoder for the codec
    codec = avcodec_find_decoder(codecParams->codec_id);
    if (codec == NULL) {
        printf("Could not find decoder for the codec\n");
        return -1;
    }

    // Step 6: Open codec
    codecContext = avcodec_alloc_context3(codec);
    if (avcodec_open2(codecContext, codec, NULL) < 0) {
        printf("Could not open codec\n");
        return -1;
    }

    // Step 7: Use the codec for decoding

    // Cleanup
    avcodec_free_context(&codecContext);
    avformat_close_input(&formatContext);

    return 0;
}