temujin July 19, 2017 at 20:59

Taming multimedia with ffmpeg

Suddenly, your drive to the eyeballs is packed with photos and videos, and new trips are ahead. What to do, buy a new one, rent disk space on the cloud, or can it be better to compress video files through ffmpeg ?

But why limit yourself to save disk space? I propose to learn the amazing possibilities of processing photos, audio and video data, command line utilities.

Ffmpeg library and video processing

The open source library ffmpeg is most likely already installed on your operating system. If not, install it with a standard package management program, it will not take much time.

Convert one audio and video file format to another

ffmpeg -i file. [options] file.

Reduce the video recorded on the camera:

ffmpeg -i MVI_4703.MOV MVI_4703.avi

The same, but with quality control.

ffmpeg -i MVI_4703.MOV -q:v 4 MVI_4703.avi

The video size has decreased by more than 5 times without a noticeable loss in quality. The option -qscale:v n, in short, -q:v nallows you to set the quality level of the generated video stream, where it ntakes values in the range from 1 to 31. A value of 1 corresponds to the best quality, and 31 to the worst.

-rw-r--r-- 1 mig users 124M июл 18 23:29 foto/MVI_4703.avi
-rw-r--r-- 1 mig users 686M июн 27 21:38 foto/MVI_4703.MOV

Specify codec

In order to select the codec we need, we use the keys .-c:a -c:v

ffmpeg -i video.mp4 -c:v vp9 -c:a libvorbis video.mkv

You can see all supported codecs using the command ffmpeg -codecs.

Change file container

Now take this ~~user case~~happening. The built-in player of your TV supports mkv format but does not support m4v. In order to change the container, use the following command.

ffmpeg -i video.m4v -c:av copy video.mkv

If you need to change only the sound and leave the video as it is, run this command. For some reason, Philips TVs only understand AAC / AC3 audio formats.

ffmpeg -i video.m4v -c:v copy -c:a aac video.mkv

Add soundtrack

Just list the input files and set the output.

ffmpeg -i video.mp4 -i audio.ogg video_sound.mp4

Extract audio track

If you just need to extract the sound, then you can.

ffmpeg -i video.MOV -vn audio.ogg

Set the format of the extracted audio track.

ffmpeg -i video.MOV -vn -c:a flac audio.flac

Indicates an acceptable bitrate, by default 128k will be recorded.

ffmpeg -i video.MOV -vn -c:a flac -b:a 192k audio.flac

Making a slide show of pictures

This is the case when it was smooth on paper. In practice, you have to walk a rake, wading through a variety of formats, codecs, sizes and orientations of photos.

ffmpeg -r .3 -pix_fmt rgba -s 1280x720 -pattern_type glob -i "*.JPGЭ video.mkv

Some clarification required.

-r number - frame rate per second.
-pix_fmt - Pixel format, list from the command ffmpeg -pix_fmts. Not with all formats it turns out to set the desired frame size.
-pattern_type glob - To use pattern matching as in a command shell. An alternative is to use the C format printf, for example image%03d.pngfor everyone image0001.png, image0002.pngetc.

Change Video Stream

Suppose you do not need the entire video file, but only part of it. This command will cut 10 seconds of video, starting from the first minute.

ffmpeg -i video_full.m4v -c:av copy -ss 00:01:00 -t 10 video_short.m4v

How to improve the quality of audio or video streams? For this, a bitrate key is used -b.

ffmpeg - video.webm -c:a copy -c:v vp9 -b:v 2M final.mkv

Screen capture

A device is used to capture the screen x11grab, and ffmpeg must be compiled with the option --enable-x11grab.

ffmpeg -f x11grab -framerate 25 -video_size 4cif -i :0.0 out.mpg

-video_size word - Capture size, cif = 352x288, 4cif = 704x576. More in info ffmpeg-utils.

Bonus track

For automatic photo processing, it is convenient to work with ImageMagick . Resize all photos in a folder.

mogrify -resize 60% *.png

Accurate image sharpening, like Smart Sharpen using a Perl script that uses convertand compositea set of tools of ImageMagick .