What is the method for C language to call ffmpeg?

The method for calling the ffmpeg library in the C language is to use the API functions provided by FFmpeg. Here are the basic steps for using the FFmpeg library for audio and video processing:

1. Include the FFmpeg header file:

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

1. Initialise the FFmpeg library.

av_register_all();

1. Open the input file:

AVFormatContext *formatContext = NULL;
if(avformat_open_input(&formatContext, inputFileName, NULL, NULL) != 0) {
    // 打开文件失败，处理错误
}

1. Retrieve audio and video stream information:

if (avformat_find_stream_info(formatContext, NULL) < 0) {
    // 获取流信息失败，处理错误
}

1. Search for video and audio streams:

int videoStreamIndex = -1;
int audioStreamIndex = -1;
for (int i = 0; i < formatContext->nb_streams; i++) {
    if (formatContext->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
        videoStreamIndex = i;
    } else if (formatContext->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
        audioStreamIndex = i;
    }
}

1. Open the video decoder:

AVCodecContext *videoCodecContext = avcodec_alloc_context3(NULL);
avcodec_parameters_to_context(videoCodecContext, formatContext->streams[videoStreamIndex]->codecpar);
AVCodec *videoCodec = avcodec_find_decoder(videoCodecContext->codec_id);
avcodec_open2(videoCodecContext, videoCodec, NULL);

1. Decode video frames.

AVPacket *packet = av_packet_alloc();
AVFrame *frame = av_frame_alloc();
while (av_read_frame(formatContext, packet) >= 0) {
    if (packet->stream_index == videoStreamIndex) {
        avcodec_send_packet(videoCodecContext, packet);
        while (avcodec_receive_frame(videoCodecContext, frame) == 0) {
            // 处理视频帧数据
        }
    }
    av_packet_unref(packet);
}

1. Close the decoder, close the input file.

avcodec_free_context(&videoCodecContext);
avformat_close_input(&formatContext);

These are just the basic operations for audio and video processing using the FFmpeg library, the specific usage and capabilities can be adjusted as needed. Additionally, other API functions provided by FFmpeg can also be used for tasks such as audio and video encoding, packaging, and filtering.