一、通過此文可以得到什么

通過此練習：

• 1、知道了如何計算一個音頻和視頻的播放時間；
• 2、知道了音視頻解碼的思路的大體流程，之后無非就是在這個流程上進行擴充細節；
• 3、知道了如何通過C語言或者C++編程語言結合ffmpeg拿到一些音視頻的關鍵資訊，例如：幀率等；

二、實作思路

三、實作效果

zhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ make
make all
make[1]: 進入目錄“/data/project/VSCProject/ffmpegStudy/src”
Compiling main.cpp to main.o ..
cp hello /data/project/VSCProject/ffmpegStudy/src/../
# make 【hello】 finish !!!	
make[1]: 離開目錄“/data/project/VSCProject/ffmpegStudy/src”
zhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ 
zhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ ./hello 
Hello World !
decode video fileName=/home/zhenghui/視頻/1080P.mp4 
[NULL @ 0x5654cc332d80] Opening '/home/zhenghui/視頻/1080P.mp4' for reading
[file @ 0x5654cc333380] Setting default whitelist 'file,crypto,data'
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Format mov,mp4,m4a,3gp,3g2,mj2 probed with size=2048 and score=100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] ISO: File Type Major Brand: isom
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Unknown dref type 0x206c7275 size 12
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Processing st: 0, edit list 0 - media time: 1072, duration: 3621888
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Offset DTS by 1072 to make first pts zero.
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Setting codecpar->delay to 2 for stream st: 0
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Unknown dref type 0x206c7275 size 12
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Processing st: 1, edit list 0 - media time: 0, duration: 9990149
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 29.916667 0.006250
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 30.000000 0.000066
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 60.000000 0.000265
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 120.000000 0.001061
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 240.000000 0.004244
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 29.970030 0.000868
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] rfps: 59.940060 0.003473
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] Before avformat_find_stream_info() pos: 87425182 bytes read:315205 seeks:1 nb_streams:2
[h264 @ 0x5654cc3340c0] nal_unit_type: 7(SPS), nal_ref_idc: 3
[h264 @ 0x5654cc3340c0] nal_unit_type: 8(PPS), nal_ref_idc: 3
[h264 @ 0x5654cc3340c0] nal_unit_type: 7(SPS), nal_ref_idc: 3
[h264 @ 0x5654cc3340c0] nal_unit_type: 8(PPS), nal_ref_idc: 3
[h264 @ 0x5654cc3340c0] nal_unit_type: 6(SEI), nal_ref_idc: 0
[h264 @ 0x5654cc3340c0] nal_unit_type: 5(IDR), nal_ref_idc: 3
[h264 @ 0x5654cc3340c0] Format yuv420p chosen by get_format().
[h264 @ 0x5654cc3340c0] Reinit context to 1920x1088, pix_fmt: yuv420p
[h264 @ 0x5654cc3340c0] no picture 
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] All info found
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x5654cc332d80] After avformat_find_stream_info() pos: 53231 bytes read:393067 seeks:2 frames:4
video_index=0 
audio_index=1 
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/zhenghui/視頻/1080P.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
    description     : Packed by Bilibili XCoder v2.0.2
  Duration: 00:03:46.53, start: 0.000000, bitrate: 3087 kb/s
  Stream #0:0[0x1](und), 3, 1/16000: Video: h264 (High), 1 reference frame (avc1 / 0x31637661), yuv420p(progressive, left), 1920x1080 (1920x1088) [SAR 1:1 DAR 16:9], 0/1, 2951 kb/s, 30 fps, 30 tbr, 16k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1[0x2](und), 1, 1/44100: Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
media name =/home/zhenghui/視頻/1080P.mp4 
stream number: 2 
media average ratio: 3015 kbps
media total time: 0:3:46 
######## Video info: ######## 
stream index : 0 
fps:29.999914 fps
video codec : H264 
video_time : 00:03:46
######## Audio info: ######## 
stream index : 1 
stream sample_rate : 44100 Hz 
stream format : AV_SAMPLE_FMT_FLTP 
channels number:2 
audio codec:AAC 
audio_time : 00:03:46
[AVIOContext @ 0x5654cc33b7c0] Statistics: 393067 bytes read, 2 seeks
zhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ 

四、實作源代碼

0聲Darren哥牛

#include <iostream>
#include <stdio.h>


#ifdef __cplusplus //表示是一個c++程式
extern "C"{
#endif

#include <libavdevice/avdevice.h>
#include <libavutil/frame.h>
#include <libavutil/imgutils.h>
#include <libavutil/log.h>
#include <libswscale/swscale.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>

#ifdef __cplusplus
}
#endif


//g++ -I ../include/ hello_world.cpp -o hello_world -L../lib/ -lavcodec -lavdevice -lavfilter -lavformat -lavutil
void decode()
{
    char *fileName = "/home/zhenghui/視頻/1080P.mp4"; 

    printf("decode video fileName=%s \n",fileName);

    int ret = 0;
    // 1、分配解復用器背景關系
    AVFormatContext *ctx = NULL;
    ctx = avformat_alloc_context(); 

    // 2、根據url打開本地檔案或網路流
    ret = avformat_open_input(&ctx,fileName,NULL,NULL);

    if(ret < 0)
    {
        printf("打開%s失敗 ! \n",fileName);
        return;
    }

    // 3、讀取媒體的部分資料包，獲取碼流資訊
    ret = avformat_find_stream_info(ctx,NULL);
    if(ret < 0){
        printf("獲取碼流資訊失敗 !\n");
        return;
    }

    // 3、獲取音頻流和視頻流的索引
    int video_index = -1;
    int audio_index = -1;

    video_index = av_find_best_stream(ctx,AVMEDIA_TYPE_VIDEO,-1,-1,NULL,0);
    printf("video_index=%d \n",video_index);

    audio_index = av_find_best_stream(ctx,AVMEDIA_TYPE_AUDIO,-1,-1,NULL,0);
    printf("audio_index=%d \n",audio_index);

    // 列印流資訊
    av_dump_format(ctx,0,fileName,0);

    //列印媒體檔案url
    printf("media name =%s \n",ctx->url);
    //列印流數量
    printf("stream number: %d \n",ctx->nb_streams);
    //列印碼率
    printf("media average ratio: %lld kbps\n",(int64_t)(ctx->bit_rate/1024));

    //列印時長
    int total_seconds,hour,minute,second;
    //ctx->duration的單位是微妙，先轉換成秒，再進行轉換成其他的時間單位就比較簡單了
    total_seconds = (ctx->duration) / AV_TIME_BASE;
    hour = total_seconds / 3600;
    minute = (total_seconds % 3600) /60;
    second = (total_seconds % 60);

    // 檔案總時長
    printf("media total time: %d:%d:%d \n",hour,minute,second);

    //老版本查找流索引
    for(int i = 0;i < ctx->nb_streams;i++){
        AVStream  *av_stream = ctx->streams[i];

        //判斷流是什么型別
        //視頻流
        if( AVMEDIA_TYPE_VIDEO == av_stream->codecpar->codec_type)
        {
            printf("######## Video info: ######## \n");
            // 流索引
            printf("stream index : %d \n",av_stream->index);
            //幀率
            printf("fps:%lf fps\n",av_q2d(av_stream->avg_frame_rate));

            if(AV_CODEC_ID_MPEG4 == av_stream->codecpar->codec_id)
            {
                printf("video codec : MPEG4 \n");
            }
            else if(AV_CODEC_ID_H264 == av_stream->codecpar->codec_id)
            {
                printf("video codec : H264 \n");
            }else 
            {
                printf("video codec other value=%d \n", av_stream->codecpar->codec_id);
            }

            //獲取視頻總時長
            if(AV_NOPTS_VALUE != av_stream->duration)
            {
                int video_time =av_stream->duration * av_q2d(av_stream->time_base);
                printf("video_time : %02d:%02d:%02d\n" ,
                (video_time / 3600),
                (video_time % 3600) / 60,
                (video_time % 60)
                );
            }
            else{
                printf("audio duration unknown ! \n");
            }
        }
        //音頻流
        else if(AVMEDIA_TYPE_AUDIO == av_stream->codecpar->codec_type)
        {
            printf("######## Audio info: ######## \n");
            // 流索引
            printf("stream index : %d \n",av_stream->index);

            // 音頻編解碼器的采樣率 單位Hz
            printf("stream sample_rate : %d Hz \n",av_stream->codecpar->sample_rate);

            //音頻采樣格式
            if(AV_SAMPLE_FMT_FLTP == av_stream->codecpar->format)
            {
                printf("stream format : AV_SAMPLE_FMT_FLTP \n");
            }
            else  if(AV_SAMPLE_FMT_S16P == av_stream->codecpar->format)
            {
                printf("stream format : AV_SAMPLE_FMT_S16P \n");
            }else{
                printf("stream format : other； value=%d \n",av_stream->codecpar->format);
            }

            // 音頻信道數目
            printf("channels number:%d \n",av_stream->codecpar->channels);

            //音頻壓縮編碼格式
            if(AV_CODEC_ID_AAC == av_stream->codecpar->codec_id)
            {
                printf("audio codec:AAC \n");
            }else if(AV_CODEC_ID_MP3 == av_stream->codecpar->codec_id)
            {
                printf("audio codec:MP3 \n");
            }else{
                printf("audio codec : other； value=%d \n",av_stream->codecpar->codec_id);
            }

            //獲取視頻總時長
            if(AV_NOPTS_VALUE != av_stream->duration)
            {
                int audio_time =av_stream->duration * av_q2d(av_stream->time_base);
                printf("audio_time : %02d:%02d:%02d\n" ,
                (audio_time / 3600),
                (audio_time % 3600) / 60,
                (audio_time % 60)
                );
            }
            else{
                printf("audio duration unknown ! \n");
            }

            audio_index = i;
        }

    }

    if(ctx)
        avformat_close_input(&ctx);
}

int main() {
    // 設定控制臺輸出級別
    av_log_set_level(AV_LOG_DEBUG);
    // // 列印輸出字串Hello World ！
    av_log(NULL, AV_LOG_DEBUG, "%s", "Hello World !\n");

    decode();
    return 0;
}