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# 前言
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FFmpeg多媒体库支持的命令行调用分为三个模块：ffmpeg、ffprobe、ffplay。<br>
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其中ffmpeg命令行常用于音视频剪切、转码、滤镜、拼接、混音、截图等；<br>
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ffprobe用于检测多媒体流格式；ffplay用于播放视频,包括本地与网络视频。<br>
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详情可查阅FFmpeg官方文档：[ffmpeg Documentation](https://ffmpeg.org/documentation.html)<br>
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# 一、ffmpeg命令行
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## 1、命令行参数介绍
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Print help / information / capabilities:<br>
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-help show help<br>
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-version show version<br>
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-formats show available formats<br>
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-muxers show available muxers<br>
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-demuxers show available demuxers<br>
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-devices show available devices<br>
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-codecs show available codecs<br>
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-decoders show available decoders<br>
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-encoders show available encoders<br>
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-bsfs show available bit stream filters<br>
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-protocols show available protocols<br>
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-filters show available filters<br>
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-pix_fmts show available pixel formats<br>
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-sample_fmts show available audio sample formats<br>
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-hwaccels show available HW acceleration methods<br>
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Global options (affect whole program instead of just one file:<br>
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-v loglevel set logging level<br>
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-y overwrite output files<br>
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-n never overwrite output files<br>
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-filter_threads number of non-complex filter threads<br>
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-stats print progress report during encoding<br>
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-vol volume change audio volume (256=normal)<br>
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Per-file main options:<br>
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-f fmt force format<br>
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-c codec codec name<br>
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-codec codec codec name<br>
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-t duration record or transcode "duration" seconds of audio/video<br>
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-to time_stop record or transcode stop time<br>
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-fs limit_size set the limit file size in bytes<br>
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-ss time_off set the start time offset<br>
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-sseof time_off set the start time offset relative to EOF<br>
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-frames number set the number of frames to output<br>
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Video options:<br>
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-vframes number set the number of video frames to output<br>
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-r rate set frame rate (Hz value, fraction or abbreviation)<br>
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-s size set frame size (WxH or abbreviation)<br>
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-aspect aspect set aspect ratio (4:3, 16:9 or 1.3333, 1.7777)<br>
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-vn disable video<br>
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-vcodec codec force video codec ('copy' to copy stream)<br>
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-vf filter_graph set video filters<br>
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-ab bitrate audio bitrate (please use -b:a)<br>
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-b bitrate video bitrate (please use -b:v)<br>
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Audio options:<br>
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-aframes number set the number of audio frames to output<br>
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-aq quality set audio quality (codec-specific)<br>
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-ar rate set audio sampling rate (in Hz)<br>
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-ac channels set number of audio channels<br>
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-an disable audio<br>
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-acodec codec force audio codec ('copy' to copy stream)<br>
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-vol volume change audio volume (256=normal)<br>
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-af filter_graph set audio filters<br>
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Subtitle options:<br>
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-s size set frame size<br>
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-sn disable subtitle<br>
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-scodec codec force subtitle codec ('copy' to copy stream)<br>
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命令行整体格式：以ffmpeg开头，参数之间用空格隔开，每个参数key以"-"开头，后面跟着参数value，输出文件放在命令行最后。<br>
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## 2、音频常见操作
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### 2.1 音频转码
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直接转码：<br>
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ffmpeg -i input.mp3 output.m4a<br>
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指定编码器、采样率、声道数转码：<br>
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ffmpeg -i input.mp3 -acodec aac -ac 2 -ar 44100 output.m4a<br>
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### 2.2 音频剪切
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-ss 10指定从第10秒开始，-t 20代表剪切20秒<br>
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ffmpeg -i input.mp3 -ss 10 -t 20 cut.mp3<br>
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### 2.3 音频拼接
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ffmpeg -i concat:"hello.mp3|world.mp3" -acodec copy -vn concat.mp3<br>
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### 2.4 音频混音
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使用amix，参数inputs代表输入流个数，duration有longest、shortest、first三种模式，weights设置每条流音量权重占比：<br>
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ffmpeg -i hello.mp3 -i world.mp3 -filter_complex amix=inputs=2:duration=first -vn mix.mp3<br>
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使用amerge，合并成多声道输出：<br>
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ffmpeg -i hello.mp3 -i world.mp3 -filter_complex [0:a][1:a]amerge=inputs=2[aout] -map [aout] merge.mp3<br>
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### 2.5 空灵音效
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aecho接收4个参数：in_gain (0, 1]；out_gain (0, 1]；delays (0 - 90000]；decays (0 - 1.0]<br>
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ffmpeg -i input.mp3 -af aecho=0.8:0.8:1000:0.5 echo.mp3<br>
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### 2.6 惊悚音效
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tremolo接收2个参数：frequency [0.1, 20000.0]；depth (0, 1]<br>
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ffmpeg -i input.mp3 -af tremolo=5:0.9 tremolo.mp3<br>
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### 2.7 搞笑音效
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搞笑音效通过调节音速实现，使用atempo：<br>
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ffmpeg -i input.mp3 -filter_complex atempo=0.5 atempo.mp3<br>
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### 2.8 静音检测
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ffmpeg -i input.mp3 -af silencedetect=noise=0.0001 -f null -<br>
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### 2.9 修改音量
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ffmpeg -i input.mp3 -af volume=0.5 volume.mp3<br>
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### 2.10 抽取音频
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从视频抽取音频，也就是disable视频流、拷贝音频流：<br>
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ffmpeg -i input.mp4 -acodec copy -vn out.mp3<br>
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## 3、视频常见操作
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### 3.1 视频剪切
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基本剪切，指定起始时间、剪切时长：<br>
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ffmpeg -i input.mp4 -ss 10 -t 20 -codec copy cut.mp4<br>
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精确剪切，包含多音轨，-map 0代表所有track流进行剪切，-accurate_seek代表精确seek：<br>
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ffmpeg -i input.mp4 -ss 10 -accurate_seek -t 20 -map 0 -codec copy cut.mp4<br>
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### 3.2 视频转码
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使用-vcodec指定视频编码，-acodec指定音频编码，-s 640x480指定视频分辨率，<br>
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-b 200k指定码率，-r 20指定帧率，这样达到视频压缩效果：<br>
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ffmpeg -i input.mp4 -vcodec libx264 -acodec aac -s 640x480 -b 200k -r 20 transcode.mp4<br>
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### 3.3 视频截图
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使用-vframes指定截图数量，-ss指定起始时间放在-i前面，这样保证先seek到指定位置再截图。<br>
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如果是先-i指定输入文件再-ss，是从时间0开始解码，直到指定时间再截图，这样效率太低：<br>
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ffmpeg -ss 10 -i input.mp4 -f image2 -vframes 1 -an screenshot.jpg<br>
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### 3.4 图片水印
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使用-filter_complex指定位置overlay=x:y，如下所示：<br>
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ffmpeg -i input.mp4 -i logo.png -filter_complex overlay=10:20 pic_watermark.mp4<br>
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如果要灵活设置左上角、右上角、左下角、右下角位置，可以使用case语句，其中main_w代表视频宽度，<br>
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main_h代表视频高度，overlay_w代表水印宽度，overlay_h代表水印高度：<br>
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```
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public static String obtainOverlay(int offsetX, int offsetY, int location) {
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switch (location) {
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case 2:
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return "overlay='(main_w-overlay_w)-" + offsetX + ":" + offsetY + "'";
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case 3:
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return "overlay='" + offsetX + ":(main_h-overlay_h)-" + offsetY + "'";
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case 4:
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return "overlay='(main_w-overlay_w)-" + offsetX + ":(main_h-overlay_h)-" + offsetY + "'";
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case 1:
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default:
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return "overlay=" + offsetX + ":" + offsetY;
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}
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}
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public static String[] addWaterMarkImg(String inputPath, String imgPath, int location,
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int offsetXY, String outputPath) {
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String overlay = obtainOverlay(offsetXY, offsetXY, location);
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String waterMarkCmd = "ffmpeg -i %s -i %s -filter_complex %s -preset:v superfast %s";
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waterMarkCmd = String.format(waterMarkCmd, inputPath, imgPath, overlay, outputPath);
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return waterMarkCmd.split(" ");
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}
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```
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### 3.5 GIF水印
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使用-ignore_loop 0代表GIF循环显示，其他操作与图片水印一致：<br>
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ffmpeg -i input.mp4 -ignore_loop 0 -i logo.gif -filter_complex overlay=10:20 gif_mark.mp4<br>
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### 3.6 去除水印
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使用delogo命令，然后指定水印位置：<br>
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ffmpeg -i input.mp4 -filter_complex delogo=x=10:y=20:w=90:h=30 delogo.mp4<br>
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### 3.7 视频拼接
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视频拼接分为垂直拼接、水平拼接，还有前后拼接，这里主要介绍垂直与水平拼接，其中使用hstack做水平拼接，vstack做垂直拼接：<br>
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ffmpeg -i input1.mp4 -i input2.mp4 -filter_complex hstack out.mp4<br>
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### 3.8 视频翻转
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使用reverse实现视频翻转，但是处理比较耗时：<br>
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ffmpeg -i input.mp4 -vf reverse -an output.mp4<br>
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### 3.9 视频降噪
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使用-nr代表noise reduction，进行视频降噪：<br>
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ffmpeg -i in.mp4 -nr 500 out.mp4<br>
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### 3.10 视频抽帧
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ffmpeg -ss 20 -accurate_seek -t 10 -i input.mp4 -an -r 5 %3d.jpg<br>
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### 3.11 播放速度
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使用setpts设置视频速度，atempo设置音频速度：<br>
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ffmpeg -i in.mp4 -filter_complex [0:v]setpts=%.2f*PTS[v];[0:a]atempo=%.2f[a] -map [v] -map [a] out.mp4<br>
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### 3.12 旋转视频
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ffmpeg -i in.mp4 -c copy -metadata:s\:v:0 rotate=90 out.mp4<br>
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# 二、ffplay命令行
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ffplay主要用于播放视频，也可以播放网络流，示例如下：<br>
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ffplay -i beyond.mp4<br>
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# 三、ffprobe命令行
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ffprobe主要用于检测多媒体信息，包括时长、视频分辨率、帧率、音频采样率、声道数、每个stream流信息等等。<br>
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支持显示形式包括：json和xml，例如-print_format json<br>
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ffprobe -i input.mp4 -show_streams -show_format -print_format json<br>
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如果要显示每帧数据信息，使用-show_frames可以显示pts、packet_size、duration、frame_type等信息：<br>
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ffprobe -i input.mp4 -show_frames<br>
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如果只要显示视频流，使用-select_streams v。其中v代表video，a代表audio，s代表subtitle。<br>
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ffprobe -i input.mp4 -show_frames -select_streams v<br>
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