一、通过此文可以得到什么
通过此练习：
- 1、知道了如何计算一个音频和视频的播放时间；
- 2、知道了音视频解码的思路的大体流程，之后无非就是在这个流程上进行扩充细节；
- 3、知道了如何通过C语言或者C++编程语言结合ffmpeg拿到一些音视频的关键信息，例如：帧率等；
二、实现思路
三、实现效果
zhenghui@zh-pc:/data/project/VSCProject/ffmpegStudy$ make make all make[1]: 进入目录“/data/project/VSCProject/ffmpegStudy/src” Compiling main.cpp to main.o .. cp hello /data/project/VSCProject/ffmpegStudy/src/../ # make 【hello】 finish !!! make[1]: 离开目录“/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/视频/1080P.mp4 [NULL @ 0x5654cc332d80] Opening '/home/zhenghui/视频/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/视频/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/视频/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、实现源代码
#include <iostream> #include <stdio.h> #ifdef __cplusplus //表示是一个c++程序 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/视频/1080P.mp4"; printf("decode video fileName=%s \n",fileName); int ret = 0; // 1、分配解复用器上下文 AVFormatContext *ctx = NULL; ctx = avformat_alloc_context(); // 2、根据url打开本地文件或网络流 ret = avformat_open_input(&ctx,fileName,NULL,NULL); if(ret < 0) { printf("打开%s失败 ! \n",fileName); return; } // 3、读取媒体的部分数据包，获取码流信息 ret = avformat_find_stream_info(ctx,NULL); if(ret < 0){ printf("获取码流信息失败 !\n"); return; } // 3、获取音频流和视频流的索引 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); // 打印流信息 av_dump_format(ctx,0,fileName,0); //打印媒体文件url printf("media name =%s \n",ctx->url); //打印流数量 printf("stream number: %d \n",ctx->nb_streams); //打印码率 printf("media average ratio: %lld kbps\n",(int64_t)(ctx->bit_rate/1024)); //打印时长 int total_seconds,hour,minute,second; //ctx->duration的单位是微妙，先转换成秒，再进行转换成其他的时间单位就比较简单了 total_seconds = (ctx->duration) / AV_TIME_BASE; hour = total_seconds / 3600; minute = (total_seconds % 3600) /60; second = (total_seconds % 60); // 文件总时长 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]; //判断流是什么类型 //视频流 if( AVMEDIA_TYPE_VIDEO == av_stream->codecpar->codec_type) { printf("######## Video info: ######## \n"); // 流索引 printf("stream index : %d \n",av_stream->index); //帧率 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); } //获取视频总时长 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"); } } //音频流 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); // 音频编解码器的采样率 单位Hz printf("stream sample_rate : %d Hz \n",av_stream->codecpar->sample_rate); //音频采样格式 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); } // 音频信道数目 printf("channels number:%d \n",av_stream->codecpar->channels); //音频压缩编码格式 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); } //获取视频总时长 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() { // 设置控制台输出级别 av_log_set_level(AV_LOG_DEBUG); // // 打印输出字符串Hello World ！ av_log(NULL, AV_LOG_DEBUG, "%s", "Hello World !\n"); decode(); return 0; }
