Updated: Aug, 2016

If you need to do anything to digital video, it is well worth your while getting a copy of ffmpeg.

The project describes itself as

A complete, cross-platform solution to record, convert and stream audio and video.

I think of it as a video swiss-army knife that enables you to manipulate video, primarily in terms of converting between formats and reducing big files down.

Importantly, it is a commandline tool, so you will have to know how to launch a Terminal window.

Installation

I use brew, so installing is as simple as:

brew install ffmpeg --with-libvpx --with-libvorbis --with-x265 --with-faac --with-fdk-aac

Check the ffmpeg site for alternate ways.

Basics

To convert formats, one simply has to specify the input file (with -i) and the output file. The format is determined from the file extension and ffmpeg goes about its conversion process to achieve the requested output format:

ffmpeg -i input.mp4 output.avi

In the case of converting a mov file to a mp4, the internal audio and video streams actually do not need converting, just the container does. So you can ask ffmpeg to copy the streams while converting the container:

ffmpeg -i input.mov -vcodec copy -acodec copy output.mp4

Extracting Audio

Sometimes you come across a lecture video and you want to extract the audio so that you or others can listen to it on a phone or in the car. ffmpeg can do that:

ffmpeg -i lecture.mp4 -vcodec none audio.mp3

More Advanced Options

At the office we have need to convert our videos to a consistent output format and quality

ffmpeg -i input.mov -c:v libx264 -preset slow -pix_fmt yuv420p -profile:v main -movflags +faststart -crf 26 -filter:v scale=-1:720 -c:a libfdk_aac -ac 1 -ar 44100 -vbr 3 output.mp4

Breaking this down:

  • -c:v libx264 – use the x264 encoder, which enables certain other options below
  • -preset slow – presets tell the encoder how hard to work to reduce the file size, here we’re willing to spend more time converting
  • -pix_fmt yuv420p – this ensures that the video format is widely compatible
  • -profile:v main – this again ensures compatibility with a variety of devices
  • -movflags +faststart – this helps for files that are served via a web-browser
  • -crf 26 – a quality factor between 0 (lossless) to 51 (very lossy), 26-8 is a sweet-spot between file size and quality
  • -filter:v scale=-1:720 – resize any input to be 720 high and figure out the width (-1)
  • -c:a libfdk_aac – use this aac encoder
  • -ac 1 – go mono as we mostly have talking, not stereo music
  • -ar 44100 – keep the voice quality high as that is important for listeners
  • -vbr 3 – like crf, but 1 (low) to 6 (high) for audio compression

GIF file creation

If you are wanting to create a small animated gif, you can look at the instruction on this site

Speeding up audio (w/ bonus multiple files)

#!/bin/bash
for file in "$@"; do
    echo "$file"
    ffmpeg -i $file -af atempo=1.5 faster_$file
done