ffmpeg CLI examples

src: FFmpeg - Ultimate Guide | IMG.LY Blog

Hands-on with FFmpeg

In this section, we will discover and even try out some common features of FFmpeg!

For those who are just joining in: please get the example assets if you want to test out the commands shown in this chapter!

Inputs

Let’s see the common ways FFmpeg is fed with different data!

File

Of course, you have already seen that if you have a local file on your filesystem, FFmpeg is happy to read it!

ffmpeg -i bbb_sunflower_1080p_60fps_normal.mp4 -map 0:1 stereo_audio_only.wav

This command which is exactly the same as one of our previous ones just reads a local file. Really, that’s it.

Network

Did you know, that FFmpeg can open a file directly on the network?!

ffmpeg -t 5 -i http://distribution.bbb3d.renderfarming.net/video/mp4/bbb_sunflower_1080p_60fps_normal.mp4 bbb_first_5_seconds.mp4

The command above opens the file directly from the network and saves the first 5 seconds into a local file!

I wanted to spare bandwidth for these awesome guys over renderfarming.net, so I added the duration flag: -t 5. FFmpeg doesn’t even download the full video for this operation. Isn’t that wonderful?!

Webcam

FFmpeg can also open your webcam!

This is an example command for Linux:

ffmpeg -f v4l2 -framerate 25 -video_size 640x480 -t 10 -i /dev/video0 10seconds_of_webcam.webm

This would record 10 seconds of your webcam!

Accessing the webcam happens differently on different platforms. Also specifying parameters is different for each platform, so for this reason, if you’d like to access your webcam with FFmpeg, please refer to the documentation:

• Linux
• Windows
• OS X

Microphone

Let’s record some audio directly from your microphone!

List microphones:

arecord -l

Start 10 seconds of recording:

ffmpeg -f alsa -i hw:0,0 -t 10 out.wav

This command was meant to work on Linux, but you can check out how to do that on Microsoft Windows or macOS.

Pipe

Finally, FFmpeg can read from a pipe, and also output to a pipe.

On Linux, you could do something like this:

cat bbb_sunflower_1080p_60fps_normal.mp4 | ffmpeg -i - -f wav pipe:1 | pv > output.wav
 
# Alternative, without pv:
cat bbb_sunflower_1080p_60fps_normal.mp4 | ffmpeg -i - -f wav pipe:1 > output.wav

This command would use the cat program to simply read in the video file and output it to its standard output. Then this output is piped INTO FFmpeg, through its standard input. The combination “-i -” means “read from standard input”. By the way, standard input would be your keyboard otherwise, if we wouldn’t use any redirection here.

Then we specify the required output format for FFmpeg, with “-f wav”. This is needed because now we’ll have no output file name, and FFmpeg will not be able to guess the format. Then we specify “pipe:1” as an output, meaning we’d like FFmpeg to output to its standard output.

From then, we pipe the data into a program called “pv”, it is just a metering tool, that dumps information on the throughput (from its stdin to its stdout). Finally, we redirect pv’s output into a WAV file.

You might ask why we’d want to do that, why we talk about this. Piping can be useful if you build a complex pipeline from different programs or if you want to spare reading and writing to a local file.

For example, the node package fluent-ffmpeg can leverage this functionality by supplying input and output streams. For example, you can read from an S3 bucket and write to one directly.

But be warned, hell is awaiting you on that road. No kidding. You need to research the limitations of this technique. For example, many formats can not be streamed in this manner, as they need random access to the output data to write the indices at the beginning of the file after processing.

Outputs

FFmpeg can output into many protocols, from local file storage and ftp to message queue protocols all the way to streaming protocols.

For more information, check out the documentation here.