Ffmpeg audio and video unpacking

1. brief introduction

decapsulation ： As shown in the figure below , Will be FLV、MKV、MP4 Wait for the file to be unpacked into video H.264 or H.265 compressed data , Audio MP3 or AAC Of compressed data , The following figure shows the common basic operations .

2. technological process

The following figure is the basic flow chart of unpacking .

2.1 In the use of FFmpeg API Before , Need to register first API, And then you can use it API. Of course , The new version of the library does not need to call the following methods .

    av_register_all()

2.2 structure AVFormatContext

Declare the input encapsulation structure , Use the input file or stream address as the handle of the encapsulation structure . Streaming address of Korean TV station rtmp://mobliestream.c3tv.com:554/live/goodtv.sdp.

    AVFormatContext* inputFmtCtx = nullptr;
    const char* inputUrl = "rtmp://mobliestream.c3tv.com:554/live/goodtv.sdp";

    /// Open the input stream , get data  begin
    int ret = avformat_open_input(&inputFmtCtx, inputUrl, NULL, NULL);

2.3 Find audio and video stream information , Through the following interface with AVFormatContext Create the stream information corresponding to the input file .

	// lookup ;
	if (avformat_find_stream_info(inputFmtCtx, NULL) < 0)
	{
		printf("Couldn't find stream information.\n");
		return false;
	}

2.4 Read audio and video stream , use av_read_frame To read packets , The read data is stored in AVPacket in , Make sure it's audio 、 video 、 Subtitling Data , Finally decode , Or store .

	AVPacket* pkt = NULL;
	pkt = av_packet_alloc();

	while (av_read_frame(inputFmtCtx, pkt) >= 0)
	{
		// Get packets 

		//..... Decode or store 

		// Reset 
		av_packet_unref(pkt);
	}

The above code shows , Call... Through a loop av_read_frame() Read pkt package , Then you can decode or store data , If the read data ends , Then exit the loop , Start point to end operation .

2.5  Close the input file after execution , Release resources .

	// close 
	avformat_close_input(&inputFmtCtx);

	// Release resources 
	av_packet_free(&pkt);

3. Source code

int main()
{
    //av_register_all();
    avformat_network_init();

    AVDictionary* options = NULL;

    av_dict_set(&options, "buffer_size", "1024000", 0);
    av_dict_set(&options, "max_delay", "500000", 0);
    av_dict_set(&options, "stimeout", "2000000", 0);
    av_dict_set(&options, "rtsp_transport", "tcp", 0);

    AVFormatContext* inputFmtCtx = nullptr;
    const char* inputUrl = "rtmp://mobliestream.c3tv.com:554/live/goodtv.sdp";

    /// Open the input stream , get data begin
    int ret = avformat_open_input(&inputFmtCtx, inputUrl, NULL, NULL);
    if (ret != 0)
    {
        printf("Couldn't open input stream.\n");
        return -1;
    }

    int vIndex = -1;
    int aIndex = -1;

    // lookup ;
    if (avformat_find_stream_info(inputFmtCtx, NULL) < 0)
    {
        printf("Couldn't find stream information.\n");
        return false;
    }

    AVPacket* pkt = NULL;
    pkt = av_packet_alloc();

    while (av_read_frame(inputFmtCtx, pkt) >= 0)
    {
        // Get packets

        //..... Decode or store

        // Reset
        av_packet_unref(pkt);
    }

    // close
    avformat_close_input(&inputFmtCtx);

    // Release resources
    av_packet_free(&pkt);

    return 0;
}