Linux | ffmpeg

FFmpeg

FFmpeg 是一個開放原始碼的自由軟件，可以執行音頻和視像多種格式的錄影、轉檔、串流功能，包含了libavcodec ——這是一個用於多個專案中音頻和視像的解碼器函式庫，以及libavformat——一個音頻與視像格式轉換函式庫。該專案的名稱靈感來源於 MPEG 影片標準組織，其中「FF」代表「快進」（fast forward），因此FFmpeg代表「快進動態圖像專家組」。其標誌是一個之字形掃描圖案，顯示了 MPEG 影片編解碼器如何處理熵編碼。

動態影像專家小組（英語：Moving Picture Experts Group，簡稱MPEG）為一源自國際標準化組織 (ISO) 與國際電工委員會 (IEC) 等國際組織的工作小組，成立於1988年，有超過300名專家一起制定影音壓縮及傳輸的規格標準。

此計劃由幾個元件組成：命令列應用程式

• ffmpeg : 用於對視訊檔案或音頻檔案轉換格式
• ffplay : 一個簡單的播放器，基於SDL與FFmpeg函式庫
• ffprobe : 用於顯示媒體檔案的資訊

Convert mp4 to gif

ffmpeg -i input.mp4 -pix_fmt rgb24 output.gif
ffmpeg -i input.mp4 -pix_fmt gray output.gif

Cut/trim a video

The fastest and best ffmpeg-based method I have figured out is:

ffmpeg -ss 00:01:00 -to 00:08:00 -i input.mp4 -c:v copy -c:a copy output.mp4

This command trims your video in seconds!

Also, the -t option specifies a duration, not an end time. The above command will encode 7s of video starting at 1s. To start at 1s and end at 8s use -t 7. If you are using a current version of ffmpeg you can also replace -t with -to in the above command to end at the specified time.

The -c:v copy -c:a copy commands copy the original audio and video without re-encoding.

Change the output frame rate

To change the output frame rate to 30 fps, use the following command: docs

ffmpeg -i <input> -filter:v fps=30 <output>

Speeding up/slowing down video

To double the speed of the video with the setpts filter, you can use: or
To slow down your video, you have to use a multiplier greater than 1:

ffmpeg -i input.mp4 -filter:v "setpts=0.5*PTS" output.mp4
ffmpeg -i input.mp4 -filter:v "setpts=2.0*PTS" output.mp4

Compress video

H264 codec and MP4 container

To convert the MOV file to MP4 and compress it using the H.264 codec run the following command from the folder you saved the input.mov sample file:

ffmpeg -i input.mov -c:v libx264 -pix_fmt yuv420p output.mp4

• -i input.mov : - specifies the input video file.
• -c:v libx264 : - sets the video compression codec to H.264 (libx264).
• -pix_fmt yuv420p : - changes the ProRes pixel format (4:2:2) to H.264 compatible pixel format (4:2:0). output.mp4 - the name of the output file.

H265 codec and MP4 container

ffmpeg -i input.mov -c:v libx265 -pix_fmt yuv420p output.mp4

Using Constant Rate Factor (CRF) to compress the video

The command looks like this, with the -crf 28 option added:

ffmpeg -i input.mov -c:v libx264 -pix_fmt yuv420p -crf 28 output.mp4

Optimising the compression and encoding settings

There are many other command-line options that we can use to configure how FFmpeg performs the compression. Consider this command:

ffmpeg -i input.mov -c:v libx264  -pix_fmt yuv420p -crf 28 -preset fast -tune zerolatency -c:a aac output.mp4

Compress video by reducing the resolution

Reducing the video width and height (input.mov file is 1920px x 1080px,)

ffmpeg -i input.mov -c:v libx264 -pix_fmt yuv420p -crf 28 -vf scale=1280:720 output.mp4

It is also common to maintain the aspect ratio of the video so it does not become distorted. To do this we can use the scale filter with a -1 value, which will automatically calculate the correct height or width based on the other dimension. Like this:

ffmpeg -i input.mov -c:v libx264 -pix_fmt yuv420p -crf 28 -vf scale=-1:720 output.mp4

This will resize the height to 720px, while maintaining the original aspect ratio of the video.

Compress video by reducing the bitrate

Reducing video bitrate

ffmpeg -i input.mov -c:v libx264 -pix_fmt yuv420p -b:v 1000k -vf scale=-1:720 output.mp4

Here, we replace the -crf parameter and use the -b:v 1000k option to set the video bitrate to 1000 Kbps.

Reducing audio bitrate

ffmpeg -i input.mov -c:v libx264 -pix_fmt yuv420p -b:v 1000k -b:a 128k -vf scale=-1:720 output.mp4

We added the -b:a 128k to set the audio bitrate to 128 Kbps. This won't have any effect on our sample video as it doesn't have any audio.

References

1. ffmpeg.org | Documentation
2. How to compress video using FFmpeg