document/TranslateProject
2
0
Fork 0
mirror of https://github.com/LCTT/TranslateProject.git synced 2024-12-23 21:20:42 +08:00
Code Issues Packages Projects Releases Wiki Activity

Translated (#13884)

Browse Source
This commit is contained in:
郑 2019-05-31 22:27:19 +08:00 committed by MjSeven
parent 741ba60936
commit 9324e4766b
2 changed files with 496 additions and 497 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

497
sources/tech/20190527 20- FFmpeg Commands For Beginners.md
View File

@ -1,497 +0,0 @@
[#]: collector: (lujun9972)
[#]: translator: (robsean)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (20+ FFmpeg Commands For Beginners)
[#]: via: (https://www.ostechnix.com/20-ffmpeg-commands-beginners/)
[#]: author: (sk https://www.ostechnix.com/author/sk/)
20+ FFmpeg Commands For Beginners
======
![FFmpeg Commands][1]
In this guide, I will be explaining how to use FFmpeg multimedia framework to do various audio, video transcoding and conversion operations with examples. I have compiled most commonly and frequently used 20+ FFmpeg commands for beginners. I will keep updating this guide by adding more examples from time to time. Please bookmark this guide and come back in a while to check for the updates. Let us get started, shall we? If you haven’t installed FFmpeg in your Linux system yet, refer the following guide.
* [**Install FFmpeg in Linux**][2]
### 20+ FFmpeg Commands For Beginners
The typical syntax of the FFmpeg command is:
```
ffmpeg [global_options] {[input_file_options] -i input_url} ...
{[output_file_options] output_url} ...
```
We are now going to see some important and useful FFmpeg commands.
##### **1\. Getting audio/video file information**
To display your media file details, run:
```
$ ffmpeg -i video.mp4
```
**Sample output:**
```
ffmpeg version n4.1.3 Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 8.2.1 (GCC) 20181127
configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
libavutil 56. 22.100 / 56. 22.100
libavcodec 58. 35.100 / 58. 35.100
libavformat 58. 20.100 / 58. 20.100
libavdevice 58. 5.100 / 58. 5.100
libavfilter 7. 40.101 / 7. 40.101
libswscale 5. 3.100 / 5. 3.100
libswresample 3. 3.100 / 3. 3.100
libpostproc 55. 3.100 / 55. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'video.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.20.100
Duration: 00:00:28.79, start: 0.000000, bitrate: 454 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, smpte170m/bt470bg/smpte170m), 1920x1080 [SAR 1:1 DAR 16:9], 318 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : ISO Media file produced by Google Inc. Created on: 04/08/2019.
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
handler_name : ISO Media file produced by Google Inc. Created on: 04/08/2019.
At least one output file must be specified
```
As you see in the above output, FFmpeg displays the media file information along with FFmpeg details such as version, configuration details, copyright notice, build and library options etc.
If you don’t want to see the FFmpeg banner and other details, but only the media file information, use **-hide_banner** flag like below.
```
$ ffmpeg -i video.mp4 -hide_banner
```
**Sample output:**
![][3]
View audio, video file information using FFMpeg
See? Now, it displays only the media file details.
** **Recommended Download** – [**Free Guide: “Spotify Music Streaming: The Unofficial Guide”**][4]
##### **2\. Converting video files to different formats**
FFmpeg is powerful audio and video converter, so It’s possible to convert media files between different formats. Say for example, to convert **mp4 file to avi file** , run:
```
$ ffmpeg -i video.mp4 video.avi
```
Similarly, you can convert media files to any format of your choice.
For example, to convert youtube **flv** format videos to **mpeg** format, run:
```
$ ffmpeg -i video.flv video.mpeg
```
If you want to preserve the quality of your source video file, use ‘-qscale 0’ parameter:
```
$ ffmpeg -i input.webm -qscale 0 output.mp4
```
To check list of supported formats by FFmpeg, run:
```
$ ffmpeg -formats
```
##### **3\. Converting video files to audio files**
To convert a video file to audio file, just specify the output format as .mp3, or .ogg, or any other audio formats.
The above command will convert **input.mp4** video file to **output.mp3** audio file.
```
$ ffmpeg -i input.mp4 -vn output.mp3
```
Also, you can use various audio transcoding options to the output file as shown below.
```
$ ffmpeg -i input.mp4 -vn -ar 44100 -ac 2 -ab 320 -f mp3 output.mp3
```
Here,
* **-vn** – Indicates that we have disabled video recording in the output file.
* **-ar** – Set the audio frequency of the output file. The common values used are 22050, 44100, 48000 Hz.
* **-ac** – Set the number of audio channels.
* **-ab** – Indicates the audio bitrate.
* **-f** – Output file format. In our case, it’s mp3 format.
##### **4\. Change resolution of video files**
If you want to set a particular resolution to a video file, you can use following command:
```
$ ffmpeg -i input.mp4 -filter:v scale=1280:720 -c:a copy output.mp4
```
Or,
```
$ ffmpeg -i input.mp4 -s 1280x720 -c:a copy output.mp4
```
The above command will set the resolution of the given video file to 1280×720.
Similarly, to convert the above file to 640×480 size, run:
```
$ ffmpeg -i input.mp4 -filter:v scale=640:480 -c:a copy output.mp4
```
Or,
```
$ ffmpeg -i input.mp4 -s 640x480 -c:a copy output.mp4
```
This trick will help you to scale your video files to smaller display devices such as tablets and mobiles.
##### **5\. Compressing video files**
It is always an good idea to reduce the media files size to lower size to save the harddrive’s space.
The following command will compress and reduce the output file’s size.
```
$ ffmpeg -i input.mp4 -vf scale=1280:-1 -c:v libx264 -preset veryslow -crf 24 output.mp4
```
Please note that you will lose the quality if you try to reduce the video file size. You can lower that **crf** value to **23** or lower if **24** is too aggressive.
You could also transcode the audio down a bit and make it stereo to reduce the size by including the following options.
```
-ac 2 -c:a aac -strict -2 -b:a 128k
```
** **Recommended Download** – [**Free Guide: “PLEX, a Manual: Your Media, With Style”**][5]
##### **6\. Compressing Audio files**
Just like compressing video files, you can also compress audio files using **-ab** flag in order to save some disk space.
Let us say you have an audio file of 320 kbps bitrate. You want to compress it by changing the bitrate to any lower value like below.
```
$ ffmpeg -i input.mp3 -ab 128 output.mp3
```
The list of various available audio bitrates are:
1. 96kbps
2. 112kbps
3. 128kbps
4. 160kbps
5. 192kbps
6. 256kbps
7. 320kbps
##### **7. Removing audio stream from a video file
**
If you don’t want to a audio from a video file, use **-an** flag.
```
$ ffmpeg -i input.mp4 -an output.mp4
```
Here, ‘an’ indicates no audio recording.
The above command will undo all audio related flags, because we don’t audio from the input.mp4.
##### **8\. Removing video stream from a media file**
Similarly, if you don’t want video stream, you could easily remove it from the media file using ‘vn’ flag. vn stands for no video recording. In other words, this command converts the given media file into audio file.
The following command will remove the video from the given media file.
```
$ ffmpeg -i input.mp4 -vn output.mp3
```
You can also mention the output file’s bitrate using ‘-ab’ flag as shown in the following example.
```
$ ffmpeg -i input.mp4 -vn -ab 320 output.mp3
```
##### **9. Extracting images from the video **
Another useful feature of FFmpeg is we can easily extract images from a video file. This could be very useful, if you want to create a photo album from a video file.
To extract images from a video file, use the following command:
```
$ ffmpeg -i input.mp4 -r 1 -f image2 image-%2d.png
```
Here,
* **-r** – Set the frame rate. I.e the number of frames to be extracted into images per second. The default value is **25**.
* **-f** – Indicates the output format i.e image format in our case.
* **image-%2d.png** – Indicates how we want to name the extracted images. In this case, the names should start like image-01.png, image-02.png, image-03.png and so on. If you use %3d, then the name of images will start like image-001.png, image-002.png and so on.
##### **10\. Cropping videos**
FFMpeg allows to crop a given media file in any dimension of our choice.
The syntax to crop a vide ofile is given below:
```
ffmpeg -i input.mp4 -filter:v "crop=w:h:x:y" output.mp4
```
Here,
* **input.mp4** – source video file.
* **-filter:v** – Indicates the video filter.
* **crop** – Indicates crop filter.
* **w** – **Width** of the rectangle that we want to crop from the source video.
* **h** – Height of the rectangle.
* **x** – **x coordinate** of the rectangle that we want to crop from the source video.
* **y** – y coordinate of the rectangle.
Let us say you want to a video with a **width of 640 pixels** and a **height of 480 pixels** , from the **position (200,150)** , the command would be:
```
$ ffmpeg -i input.mp4 -filter:v "crop=640:480:200:150" output.mp4
```
Please note that cropping videos will affect the quality. Do not do this unless it is necessary.
##### **11\. Convert a specific portion of a video**
Sometimes, you might want to convert only a specific portion of the video file to different format. Say for example, the following command will convert the **first 50 seconds** of given video.mp4 file to video.avi format.
```
$ ffmpeg -i input.mp4 -t 10 output.avi
```
Here, we specify the the time in seconds. Also, it is possible to specify the time in **hh.mm.ss** format.
##### **12\. Set the aspect ratio to video**
You can set the aspect ration to a video file using **-aspect** flag like below.
```
$ ffmpeg -i input.mp4 -aspect 16:9 output.mp4
```
The commonly used aspect ratios are:
* 16:9
* 4:3
* 16:10
* 5:4
* 2:21:1
* 2:35:1
* 2:39:1
##### **13\. Adding poster image to audio files**
You can add the poster images to your files, so that the images will be displayed while playing the audio files. This could be useful to host audio files in Video hosting or sharing websites.
```
$ ffmpeg -loop 1 -i inputimage.jpg -i inputaudio.mp3 -c:v libx264 -c:a aac -strict experimental -b:a 192k -shortest output.mp4
```
##### **14. Trim a media file using start and stop times
**
To trim down a video to smaller clip using start and stop times, we can use the following command.
```
$ ffmpeg -i input.mp4 -ss 00:00:50 -codec copy -t 50 output.mp4
```
Here,
* –s – Indicates the starting time of the video clip. In our example, starting time is the 50th second.
* -t – Indicates the total time duration.
This is very helpful when you want to cut a part from an audio or video file using starting and ending time.
Similarly, we can trim down the audio file like below.
```
$ ffmpeg -i audio.mp3 -ss 00:01:54 -to 00:06:53 -c copy output.mp3
```
##### **15\. Split video files into multiple parts**
Some websites will allow you to upload only a specific size of video. In such cases, you can split the large video files into multiple smaller parts like below.
```
$ ffmpeg -i input.mp4 -t 00:00:30 -c copy part1.mp4 -ss 00:00:30 -codec copy part2.mp4
```
Here, **-t 00:00:30** indicates a part that is created from the start of the video to the 30th second of video. **-ss 00:00:30** shows the starting time stamp for the next part of video. It means that the 2nd part will start from the 30th second and will continue up to the end of the original video file.
** **Recommended Download** – [**Free Guide: “How to Start Your Own Successful Podcast”**][6]
##### **16\. Joining or merging multiple video parts into one**
FFmpeg will also join the multiple video parts and create a single video file.
Create **join.txt** file that contains the exact paths of the files that you want to join. All files should be same format (same codec). The path name of all files should be mentioned one by one like below.
```
file /home/sk/myvideos/part1.mp4
file /home/sk/myvideos/part2.mp4
file /home/sk/myvideos/part3.mp4
file /home/sk/myvideos/part4.mp4
```
Now, join all files using command:
```
$ ffmpeg -f concat -i join.txt -c copy output.mp4
```
If you get an error something like below;
```
[concat @ 0x555fed174cc0] Unsafe file name '/path/to/mp4'
join.txt: Operation not permitted
```
Add **“-safe 0”** :
```
$ ffmpeg -f concat -safe 0 -i join.txt -c copy output.mp4
```
The above command will join part1.mp4, part2.mp4, part3.mp4, and part4.mp4 files into a single file called “output.mp4”.
##### **17\. Add subtitles to a video file**
We can also add subtitles to a video file using FFmpeg. Download the correct subtitle for your video and add it your video as shown below.
```
$ fmpeg -i input.mp4 -i subtitle.srt -map 0 -map 1 -c copy -c:v libx264 -crf 23 -preset veryfast output.mp4
```
##### **18\. Preview or test video or audio files**
You might want to preview to verify or test whether the output file has been properly transcoded or not. To do so, you can play it from your Terminal with command:
```
$ ffplay video.mp4
```
[![][1]][7]
Similarly, you can test the audio files as shown below.
```
$ ffplay audio.mp3
```
[![][1]][8]
##### **19\. Increase/decrease video playback speed**
FFmpeg allows you to adjust the video playback speed.
To increase the video playback speed, run:
```
$ ffmpeg -i input.mp4 -vf "setpts=0.5*PTS" output.mp4
```
The command will double the speed of the video.
To slow down your video, you need to use a multiplier **greater than 1**. To decrease playback speed, run:
```
$ ffmpeg -i input.mp4 -vf "setpts=4.0*PTS" output.mp4
```
##### **20. Create Animated GIF
**
We use GIF images on almost all social and professional networks for various purposes. Using FFmpeg, we can easily and quickly create animated video files. The following guide explains how to create an animated GIF file using FFmpeg and ImageMagick in Unix-like systems.
* [**How To Create Animated GIF In Linux**][9]
##### **21.** Create videos from PDF files
I collected many PDF files, mostly Linux tutorials, over the years and saved in my Tablet PC. Sometimes I feel too lazy to read them from the tablet. So, I decided to create a video from PDF files and watch it in a big screen devices like a TV or a Computer. If you ever wondered how to make a movie file from a collection of PDF files, the following guide will help.
* [**How To Create A Video From PDF Files In Linux**][10]
##### **22\. Getting help**
In this guide, I have covered the most commonly used FFmpeg commands. It has a lot more different options to do various advanced functions. To learn more about it, refer the man page.
```
$ man ffmpeg
```
And, that’s all. I hope this guide will help you to getting started with FFmpeg. If you find this guide useful, please share it on your social, and professional networks. More good stuffs to come. Stay tuned!
Cheers!
--------------------------------------------------------------------------------
via: https://www.ostechnix.com/20-ffmpeg-commands-beginners/
作者：[sk][a]
选题：[lujun9972][b]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://www.ostechnix.com/author/sk/
[b]: https://github.com/lujun9972
[1]: https://www.ostechnix.com/wp-content/uploads/2017/05/FFmpeg-Commands-720x340.png
[2]: https://www.ostechnix.com/install-ffmpeg-linux/
[3]: http://www.ostechnix.com/wp-content/uploads/2017/05/sk@sk_001.png
[4]: https://ostechnix.tradepub.com/free/w_make141/prgm.cgi
[5]: https://ostechnix.tradepub.com/free/w_make75/prgm.cgi
[6]: https://ostechnix.tradepub.com/free/w_make235/prgm.cgi
[7]: http://www.ostechnix.com/wp-content/uploads/2017/05/Menu_004.png
[8]: http://www.ostechnix.com/wp-content/uploads/2017/05/Menu_005-3.png
[9]: https://www.ostechnix.com/create-animated-gif-ubuntu-16-04/
[10]: https://www.ostechnix.com/create-video-pdf-files-linux/

496
translated/tech/20190527 20- FFmpeg Commands For Beginners.md Normal file
View File

@ -0,0 +1,496 @@
[#]: collector: (lujun9972)
[#]: translator: (robsean)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (20+ FFmpeg Commands For Beginners)
[#]: via: (https://www.ostechnix.com/20-ffmpeg-commands-beginners/)
[#]: author: (sk https://www.ostechnix.com/author/sk/)
针对初学者的20多个 FFmpeg 命令
======
![FFmpeg Commands][1]
在这个指南中，我将阐明如何使用 FFmpeg 多多媒体框架来做各种各样的音频，视频转换编码和转换操作示例。我已经为初学者编写最通常频繁使用的20多个 FFmpeg 命令，我将通过不是地添加更多的示例来保持更新这个指南。请给这个指南加书签，以后回来检查更新。让我们开始吧？如果你还没有在你的 Linux 系统中安装 FFmpeg ，参考下面的指南。
* [**在 Linux 中安装 FFmpeg**][2]
### 针对初学者的20多个 FFmpeg 命令
FFmpeg 命令的典型语法是：
```
ffmpeg [全局选项] {[输入文件选项] -i 输入url地址} ...
{[输出文件选项] 输出url地址} ...
```
现在我们将查看一些重要的和有用的 FFmpeg 命令。
##### **1\. 获取音频/视频文件信息**
为显示你的多媒体文件细节，运行：
```
$ ffmpeg -i video.mp4
```
**样本输出：**
```
ffmpeg version n4.1.3 Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 8.2.1 (GCC) 20181127
configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
libavutil 56. 22.100 / 56. 22.100
libavcodec 58. 35.100 / 58. 35.100
libavformat 58. 20.100 / 58. 20.100
libavdevice 58. 5.100 / 58. 5.100
libavfilter 7. 40.101 / 7. 40.101
libswscale 5. 3.100 / 5. 3.100
libswresample 3. 3.100 / 3. 3.100
libpostproc 55. 3.100 / 55. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'video.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.20.100
Duration: 00:00:28.79, start: 0.000000, bitrate: 454 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, smpte170m/bt470bg/smpte170m), 1920x1080 [SAR 1:1 DAR 16:9], 318 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : ISO Media file produced by Google Inc. Created on: 04/08/2019.
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
handler_name : ISO Media file produced by Google Inc. Created on: 04/08/2019.
At least one output file must be specified
```
如你在上面的输出中看到的，FFmpeg 显示多媒体文件信息，以及 FFmpeg 细节，例如版本，配置细节，版权标记，构建和库选项等等。
如果你不想看 FFmpeg 标语和其它细节，而仅仅想看多媒体文件信息，使用 **-hide_banner** 标示，像下面。
```
$ ffmpeg -i video.mp4 -hide_banner
```
**样本输出：**
![][3]
使用 FFMpeg 查看音频，视频文件信息。
看见了吗？现在，它仅显示多媒体文件细节。
** **推荐下载** – [**免费指南：“Spotify 音乐流：非官方指南”**][4]
##### **2\. 转换视频文件到不同的格式**
FFmpeg 是强有力的音频和视频转换器，因此，在不同格式之间转换多媒体文件是可能的。以示例说明，转换 **mp4 文件到 avi 文件**，运行：
```
$ ffmpeg -i video.mp4 video.avi
```
类似地，你可以转换多媒体文件到你选择的任何格式。
例如，为转换 youtube **flv** 格式视频为 **mpeg** 格式，运行：
```
$ ffmpeg -i video.flv video.mpeg
```
如果你想维持你的源视频文件的质量，使用 “-qscale 0” 参数：
```
$ ffmpeg -i input.webm -qscale 0 output.mp4
```
为检查 FFmpeg 的支持列表，运行：
```
$ ffmpeg -formats
```
##### **3\. 转换视频文件到音频文件**
我转换一个视频文件到音频文件，只需具体指明输出格式，像 .mp3，或 .ogg，或其它任意音频格式。
上面的命令将转换 **input.mp4** 视频文件到 **output.mp3** 音频文件。
```
$ ffmpeg -i input.mp4 -vn output.mp3
```
此外，你也可以使用各种各样的音频转换编码选项到输出文件，像下面演示。
```
$ ffmpeg -i input.mp4 -vn -ar 44100 -ac 2 -ab 320 -f mp3 output.mp3
```
在这里，
* **-vn** – 表明我们已经在输出文件中禁用视频录制。
* **-ar** – 设置输出文件的音频频率。通常使用的值是22050，44100，48000 Hz。
* **-ac** – 设置音频通道的数目。
* **-ab** – 表明音频比特率。
* **-f** – 输出文件格式。在我们的实例中，它是 mp3 格式。
##### **4\. 更改视频文件的分辨率**
如果你想设置一个具体的分辨率到一个视频文件中，你可以使用下面的命令：
```
$ ffmpeg -i input.mp4 -filter:v scale=1280:720 -c:a copy output.mp4
```
或，
```
$ ffmpeg -i input.mp4 -s 1280x720 -c:a copy output.mp4
```
上面的命令将设置所给定视频文件的分辨率到1280×720。
类似地，为转换上面的文件到640×480大小，运行：
```
$ ffmpeg -i input.mp4 -filter:v scale=640:480 -c:a copy output.mp4
```
或者，
```
$ ffmpeg -i input.mp4 -s 640x480 -c:a copy output.mp4
```
这个技巧将帮助你缩放你的视频文件到较小的显示设备，例如平板电脑和手机。
##### **5\. 压缩视频文件**
减小多媒体文件的大小到较低大小来节省硬件的空间总是一个好主意.
下面的命令将压缩和减少输出文件的大小。
```
$ ffmpeg -i input.mp4 -vf scale=1280:-1 -c:v libx264 -preset veryslow -crf 24 output.mp4
```
请注意，如果你尝试减小视频文件的大小，你将丢失视频质量。如果 **24** 太有侵略性，你可以降低 **crf** 值到或更低值。
你也可以转换编码音频向下一点结果是使其有立体声感，通过包含下面的选项来减小大小。
```
-ac 2 -c:a aac -strict -2 -b:a 128k
```
** **推荐下载** – [**免费指南： “PLEX, 一本手册：你的多媒体，具有样式”**][5]
##### **6\. 压缩音频文件**
正像压缩视频文件一样，为节省一些磁盘空间，你也可以使用 **-ab** 标示压缩音频文件。
例如，你有一个320 kbps 比特率的音频文件。你想通过更改比特率到任意较低的值来压缩它，像下面。
```
$ ffmpeg -i input.mp3 -ab 128 output.mp3
```
各种各样可用的音频比特率列表是：
1. 96kbps
2. 112kbps
3. 128kbps
4. 160kbps
5. 192kbps
6. 256kbps
7. 320kbps
##### **7. 从一个视频文件移除音频流**
如果你不想从一个视频文件中要一个音频，使用 **-an** 标示。
```
$ ffmpeg -i input.mp4 -an output.mp4
```
在这里，‘an’ 表示没有音频录制。
上面的命令会撤销所有音频相关的标示，因为我们没有从 input.mp4 中音频操作。
##### **8\. 从一个多媒体文件移除视频流**
类似地，如果你不想要视频流，你可以使用 ‘vn’ 标示从多媒体文件中简单地移除它。vn 代表没有视频录制。换句话说，这个里面转换所给定多媒体文件到音频文件中。
下面的命令将从所给定多媒体文件中移除视频。
```
$ ffmpeg -i input.mp4 -vn output.mp3
```
你也可以使用 ‘-ab’ 标示来提出输出文件的比特率，如下面的示例所示。
```
$ ffmpeg -i input.mp4 -vn -ab 320 output.mp3
```
##### **9. 从视频中提取图像 **
FFmpeg 的另一个有用的特色是我们可以从一个视频文件中简单地提取图像。这可能是非常有用的，如果你想从一个视频文件中创建一个相册。
为从一个视频文件中提取图像，使用下面的命令：
```
$ ffmpeg -i input.mp4 -r 1 -f image2 image-%2d.png
```
在这里，
* **-r** – 设置帧速度。即，每秒提取帧到图像的数字。默认值是 **25**。
* **-f** – 表示输出格式，即，在我们的实例中是图像。
* **image-%2d.png** – 表明我们如何想命名提取的图像。在这个实例中，命名应该开端，像这样image-01.png，image-02.png，image-03.png 等等。如果你使用 %3d ，那么图像的命名将开始，像 image-001.png，image-002.png 等等。
##### **10\. 裁剪视频**
FFMpeg 允许裁剪一个给定的多媒体文件到我们选择的任何范围。
裁剪一个视频文件的语法如下给定：
```
ffmpeg -i input.mp4 -filter:v "crop=w:h:x:y" output.mp4
```
在这里，
* **input.mp4** – 源视频文件。
* **-filter:v** – 表示视频过滤器。
* **crop** – 表示裁剪过滤器。
* **w** – 我们想自源视频中来裁剪的矩形的 **宽度** 。
* **h** – 矩形的高度。
* **x** – 我们想自源视频中来裁剪的矩形的 **x 坐标** 。
* **y** – 矩形的 y 坐标。
让我们表达，你想要一个来自视频的**位置(200,150)**，且具有**640像素的宽度**和**480像素的高度**视频, 命令应该是：
```
$ ffmpeg -i input.mp4 -filter:v "crop=640:480:200:150" output.mp4
```
请注意，剪切视频将影响质量。除非必要，请勿剪切。
##### **11\. 转换一个视频的具体的部分**
有时，你可能想仅转换视频文件的一个具体的部分到不同的格式。以示例说明，下面的命令将转换所给定视频input.mp4 文件的**第一个50秒**到视频 .avi 格式。
```
$ ffmpeg -i input.mp4 -t 10 output.avi
```
在这里，我们以秒具体说明时间。此外，以**hh.mm.ss** 格式具体说明时间也是可接受的。
##### **12\. 设置视频的屏幕高宽比**
你可以使用 **-aspect** 标示设置一个视频文件的屏幕高宽比，像下面。
```
$ ffmpeg -i input.mp4 -aspect 16:9 output.mp4
```
通常使用的 aspect 比例是：
* 16:9
* 4:3
* 16:10
* 5:4
* 2:21:1
* 2:35:1
* 2:39:1
##### **13\. 添加海报图像到音频文件**
你可以添加海报图像到你的文件，以便图像将在播放音频文件时显示。这对托管在视频托管主机或共享网站中的音频文件是有用的。
```
$ ffmpeg -loop 1 -i inputimage.jpg -i inputaudio.mp3 -c:v libx264 -c:a aac -strict experimental -b:a 192k -shortest output.mp4
```
##### **14. 使用开始和停止时间剪下一段多媒体文件
**
为剪下一段视频到小块的剪辑,使用开始和停止时间,我们可以使用下面的命令。
```
$ ffmpeg -i input.mp4 -ss 00:00:50 -codec copy -t 50 output.mp4
```
在这里，
* –s – 表示视频剪辑的开始时间。在我们的示例中，开始时间是第50秒。
* -t – 表示总的持续时间。
当你想从一个音频或视频文件剪切一部分，使用开始和结束时间是非常有帮助的
类似地，我们可以像下面剪下音频。
```
$ ffmpeg -i audio.mp3 -ss 00:01:54 -to 00:06:53 -c copy output.mp3
```
##### **15\. 分裂视频文件到多个部分**
一些网站将仅允许你上传一个具体指定大小的视频。在这样的情况下，你可以分裂大的视频文件到多个较小的部分，像下面。
```
$ ffmpeg -i input.mp4 -t 00:00:30 -c copy part1.mp4 -ss 00:00:30 -codec copy part2.mp4
```
在这里，
**-t 00:00:30** 表示从视频的开始到视频的第30秒创建一部分视频。
**-ss 00:00:30** 为视频的下一部分显示开始时间戳。它意味着第2部分将从第30秒开始，并将持续到原始视频文件的结尾。
** **推荐下载** – [**免费指南：“如何开始你自己的成功的博客”**][6]
##### **16\. 接合或合并多个视频部分到一个**
FFmpeg 也将接合多个视频部分，并创建一个单个视频文件。
创建包含你想接合文件的准确的路径的 **join.txt** 。所有的玩家应该是相同的格式（相同格式）。所有文件的路径应该依次地提到，像下面。
```
file /home/sk/myvideos/part1.mp4
file /home/sk/myvideos/part2.mp4
file /home/sk/myvideos/part3.mp4
file /home/sk/myvideos/part4.mp4
```
现在，接合所有文件，使用命令：
```
$ ffmpeg -f concat -i join.txt -c copy output.mp4
```
如果你得到一些像下面的错误；
```
[concat @ 0x555fed174cc0] Unsafe file name '/path/to/mp4'
join.txt: Operation not permitted
```
添加 **“-safe 0”** :
```
$ ffmpeg -f concat -safe 0 -i join.txt -c copy output.mp4
```
上面的命令将接合 part1.mp4，part2.mp4，part3.mp4，和 part4.mp4 文件到一个称为“output.mp4”的单个文件中。
##### **17\. 添加字幕到一个视频文件**
我们可以使用 FFmpeg 来添加字幕到一个视频文件。为你的视频下载正确的字母，并如下所示添加它到你的视频。
```
$ fmpeg -i input.mp4 -i subtitle.srt -map 0 -map 1 -c copy -c:v libx264 -crf 23 -preset veryfast output.mp4
```
##### **18\. 预览或测试视频或音频文件**
你可能希望通过预览来验证或测试输出的文件是否已经被恰当地转码编码。为完成预览，你可以从你的终端播放它，用命令：
```
$ ffplay video.mp4
```
[![][1]][7]
类似地，你可以测试音频文件，像下面所示。
```
$ ffplay audio.mp3
```
[![][1]][8]
##### **19\. 增加/减少视频播放速度**
FFmpeg 允许你调整视频播放速度。
为增加视频播放速度，运行：
```
$ ffmpeg -i input.mp4 -vf "setpts=0.5*PTS" output.mp4
```
该命令将双倍视频的速度。
为降低你的视频速度，你需要使用一个倍数 **大于 1** 。为减少播放速度，运行：
```
$ ffmpeg -i input.mp4 -vf "setpts=4.0*PTS" output.mp4
```
##### **20. 创建动画的 GIF
**
我们在几乎所有的社交和专业网络上为各种各样的目的使用 GIF 图像。使用 FFmpeg，我们可以简单地和快速地创建动画的视频文件。下面的指南阐释，如何在类 Unix 系统中使用 FFmpeg 和 ImageMagick T创建一个动画的 GIF 文件。
* [**在 Linux 中如何创建动画的 GIF**][9]
##### **21.** 从 PDF 文件中创建视频
我长年累月的收集很多 PDF 文件，大多数是 Linux 教程，保存在我的平板电脑中。有时我懒得从平板电脑中月度它们。因此，我决定从 PDF 文件中创建一个视频，在一个大屏幕设备（像一台电视机或一台电脑）中观看它们。如果你曾经想知道如何从一批 PDF 文件中制作一个电影，下面的指南将帮助你。.
* [**在 Linux 中如何从 PDF 文件中创建一个视频**][10]
##### **22\. 获取帮助**
在这个指南中，我已经覆盖大多数常常使用的 FFmpeg 命令。 它有很多不同的选项来做各种各样的高级功能。为学习更多，参考手册页。
```
$ man ffmpeg
```
然后，这就是全部。我希望这个指南将帮助你 FFmpeg 入门。如果你发现这个指南有用，请在你的社交和专业网络上分享它。更多好东西将要来。敬请期待！
谢谢！
--------------------------------------------------------------------------------
via: https://www.ostechnix.com/20-ffmpeg-commands-beginners/
作者：[sk][a]
选题：[lujun9972][b]
译者：[robsean](https://github.com/robsean)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://www.ostechnix.com/author/sk/
[b]: https://github.com/lujun9972
[1]: https://www.ostechnix.com/wp-content/uploads/2017/05/FFmpeg-Commands-720x340.png
[2]: https://www.ostechnix.com/install-ffmpeg-linux/
[3]: http://www.ostechnix.com/wp-content/uploads/2017/05/sk@sk_001.png
[4]: https://ostechnix.tradepub.com/free/w_make141/prgm.cgi
[5]: https://ostechnix.tradepub.com/free/w_make75/prgm.cgi
[6]: https://ostechnix.tradepub.com/free/w_make235/prgm.cgi
[7]: http://www.ostechnix.com/wp-content/uploads/2017/05/Menu_004.png
[8]: http://www.ostechnix.com/wp-content/uploads/2017/05/Menu_005-3.png
[9]: https://www.ostechnix.com/create-animated-gif-ubuntu-16-04/
[10]: https://www.ostechnix.com/create-video-pdf-files-linux/