Going further with FFMpeg

This is my follow up to getting started with FFmpeg. I strongly recommend getting to know the tool better in my previous post about it.

Concatenate

Multiple clips can be merged together with the concat demuxer. The idea is to create a text file with a list of files to concatenate together (in order), the format is as follows:

# List of files in order
file './file1.mp4'
file './file2.mp4'
file './file3.mp4'

For the lazy people like me it’s possible to use shell scripting to generate this list:

for f in ./*.mp4; do
  echo "file '$f'" >> list.txt
done

Then you need to feed the file as an input and specify the format (-f) as concat:

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

The wiki page speaks more in detail about this feature.

Extracting the frames

It is quite simple to extract all the frames from a video as pictures.

ffmpeg -i input.mp4 frame_%03d.png

In this command we extract every frame from input.mp4 as PNG pictures. We use the printf format for the numbering of the frame (we pad with 0 the %d for 3 characters).

It’s possible to use the parameters for the start and length of the clip to extract part of the frames or just simply limit number of frames to extract with -vframes. We can also specify a different framerate to work with during this process with -vf fps=1.

Hardware acceleration encoding

For maximum speed it is possible to use a hardware encoder for H264, I will only cover how to do this with an NVidia GPU (NVENC).

First check that FFmpeg has not been configured with --disable-nvenc, this will appear in the banner when running FFmpeg if NVENC is disabled.

ffmpeg -ss 14:01 -i "input.mp4" \
  -c:v h264_nvenc               \
  -b:v 60000k                   \
  -t 0:30
  output.mp4

This looks exactly as encoding, except the codec on line 2 is different, it has _nvenc appended to it. This is really simple and will boost the encoding drastically.

Reading more

Please check out the following pages if you wish to know more:

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SenpaiSilver

Junk food tastes good.

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