krmmzs / FFmpeg

some demo with FFmpeg

FFmpeg

Overview

• Resources
• Useful command parameters
  • video envoder
  • constant rate factor
  • video filter
  • video cropping
  • video merging
• Tips
  • merge mp4
  • Lossless cropping
  • make telegram image strikers
  • create Thumbnails
  • Add watermark
  • gif animation conversion
  • screenshot

Resources

• piaoyun/ffmpeg.mdffmpeg 视频合并、格式转换、截图

• ruanyifeng

• leandromoreira/ffmpeg-libav-tutorialtext

• How to Write a Video Player in

Useful command parameters

video envoder

-c:v

Manually specify a video encoder.

tldr

ffmpeg \
-loglevel error \
-i 1.mkv \
-c:v h264_nvenc \
output.mp4

(h264_nvenc == libx264 + NVIDIA video card(Hardware acceleration)

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -preset veryfast output.mp4

(-preset xxx) xxx:

• ultrafast(fast encoding but large file size.)
• veryfast
• faster
• fast
• medium(default)
• slow
• slower
• verslow

constant rate factor

-crf

range: 0(lossless but bigger file)-51(bad buf smaller file) often use: 19-28

tldr

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc output.mp4

video filter

-vf

tldr

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -vf "scale=1024:576" output.mp4

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -vf "scale=-1:720" output.mp4

where -1 lets ffmpeg help with the derivation

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -vf "transpose=1" output.mp4

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -vf "scale=256:256, transpose=1" output.mp4

Rotation

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -vf "crop:400:400:100:100" output.mp4

crop=w : h : x : y(wide, height, coordinates of the upper left corner)

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -vf "crop=iw/3:ih/3" output.mp4

iw(input width)

Video cropping

-ss <start time> -t <length of time> -to <end time>

tldr

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -ss 00:00:03 -t 00:00:05 output.mp4

ffmpeg -i 1.mkv -loglevel error -c:v h264_nvenc -ss 00:00:03 -to 00:00:08 output.mp4

Video merging

Need to list file names to txt file summary before merging starts mylist.txt:

    file 'clip1.mp4'
    file 'clip2.mp4'
    file 'clip3.mp4'

tldr

ffmpeg -f concat -i mylist.txt -c copy output.mp4

-c copy mern just copy, don't encoding(mp4 -> mp4).

Tips

merge mp4

ffmpeg -i "1.mp4" -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts
ffmpeg -i "2.mp4" -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate2.ts
ffmpeg -i "3.mp4" -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate3.ts
ffmpeg -i "concat:intermediate1.ts|intermediate2.ts|intermediate3.ts" -c copy -bsf:a aac_adtstoasc "output.mp4"

Lossless cropping

ffmpeg -ss START -t DURATION -i INPUT -vcodec copy -acodec copy OUTPUT

• vcodec copy
• acodec copy

表示所要使用的视频和音频的编码格式，这里指定为copy表示原样拷贝；

有可能会出现一些黑屏或者有负秒的出现: 见文章

如果copy,最好带上 -avoid_negative_ts 1

ffmpeg -ss START -t DURATION -i INPUT -vcodec copy -acodec copy -avoid_negative_ts 1 OUTPUT

make telegram image strikers

ffmpeg -i image_2022-09-18_11-02-56.png -vf scale=512:-1 1.png

telegram needs png of 512:-1

Create Thumbnails

ffmpeg -i test.mp4 -vf "fps=1/10,scale=-2:720" thumbnail-%03d.jpg

• fps=1/10 One picture every ten seconds
• scale=-2:720 the size of the image

Add watermark

ffmpeg -i test.mp4 cat.jpg -filter_complex "overlay=100:100" output.mp4

cat.jpg is watermark picture -filter_complex is filter overlay overlay cat.jpg to test.mp4 100:100 is the position of watermark in test.mp4

gif animation conversion

ffmpeg -i test.avi -ss 0 -t 3 -filter_complex [0:v]fps=15,scale=-1:256,split[a][b];[a]palettegen[p];[b][p]paletteuse output.gif

gif 不太适合太长的视频，所以剪成 3 秒的视频，用过滤器缩放视频和调整帧率 split[a][b];[a]palettegen[p];[b][p]paletteuse 是因为 gif256 色的限制，需要创建一个调色板

screenshot

每隔一秒截一张图

ffmpeg -i out.mp4 -f image2 -vf fps=fps=1 out%d.png

每隔20秒截一张图

ffmpeg -i out.mp4 -f image2 -vf fps=fps=1/20 out%d.png

Extract audio

ffmpeg \
-i input.mp4 \
-vn -c:a copy \
output.aac