More commandline help

This post contains some useful information. While I’m not interested in encouraging you to hack DVDs and make production companies suffer, we do need to find ways to extract parts of films pull their audio and perform analysis on them. Some of the information below should help. It’s been tested for OSX users, but because most of what’s advised is command line based, you can port the information below to PC or Linux.

Importing a DVD

To import a DVD to a digital file for your archives, you can use makemkv: www.makemkv.com/. This makes a .mkv container file which holds all the streams (video, audio, subtitles etc.) of your DVD. Think of it as a disc image of the DVD, it runs just like the DVD with all menus and extra options. A full DVD extraction will probably be around 8gb. The main feature, probably 4-5gb.

This format isn’t that helpful for an analysis, expecially if we wish to inspect the audio, rather it would be really nice to see the audio in Reaper, to listen to the 5.1 or stereo files and perform audio analysis on them.

Coming up…

What follows may seem reasonably convoluted for a basic user of a computer, but it’s intended to open up a universe of possiblities that will become important to you in the future. Using FFMPEG and other commandline processing tools can even save you money and bring you into much closer contact with the engines behind many of the very expensive apps, DAWs and Video editors out there.

Install xcode

If you want to use xCode on other projects, install it , but be prepared to loose lots of HDD space and time downloading it. developer.apple.com/xcode/

If you install the commandline tools, this should be quicker, it’s explained in detail here:

railsapps.github.io/xcode-command-line-tools.html

I think you should be able to open the terminal and type:

xcode-select --install

When these are installed,  you can do what follows. I realise that this is a non-trivial task, but if you’re interested in building apps for phones and are working with Unity etc. you’ll need xCode installed for iOS development anyway so, might as well bite the bullet now.

Install Homebrew

Open the terminal and paste this in:

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Above info from: trac.ffmpeg.org/wiki/CompilationGuide/MacOSX

More useful information about homebrew and how it works;

www.howtogeek.com/211541/homebrew-for-os-x-easily-installs-desktop-apps-and-terminal-utilities/

Installing FFMPEG

FFMPEG is a command line utility for converting media files. It’s powerful, fast and accurate.

In the terminal type

brew install ffmpeg

Installing Handbrake

In the terminal type

brew install handbrake

This will install handbrake and allow you to simply and quickly select chapters from the .mkv file you created from the DVD in the first place if you want to extract such.

Installing Makemkv command line

brew cask install makemkv

When you’ve got FFMPEG working and installed you can extract your film from the DVD, convert the file to something useful so you can do your analysis. I know, this is all a bit of a faff, but bear with it.

Install SoX while you’re at it

brew install sox

Extract some audio from your film for analysis

Your DVD/.mkv file will have various streams within its container, subtitles, the main film, dvd extras, and the sound for each of these extras or dubs will all be in differnt streams, so to find out which stream the audio you want is on, you first need to probe the .mkv for the right stream. So in the terminal, first navigate to the directory where your film is:

cd <path to the directory where your film is>

e.g

cd /Users/mparker/Movies/Hukkle

then

ffprobe movieName.mkv

you should get a nice pile of information printed to the terminal window.

see the kind of code you might get

You are probably interested in stream #0:1 which is most likely to have the .ac3 audio file in either stereo or 5.1. To extract that to PCM audio with the channel ordering in ITU FILM format (L,R,C,sub,Ls,Rs).

This will extract the audio of stream #0:1 to a 16bit pcm wav file in 2 channels (I think FFMPEG actually makes a down mix (removing the LFE channel))  if this is a 5.1 .ac3 file:

ffmpeg -i video.mkv -map 0:1 -acodec pcm_s16le -ac 2 audio.wav

For more channel munging FFMPEG skills read this: trac.ffmpeg.org/wiki/AudioChannelManipulation

You’ll see in the command line above, we call the FFMPEG software, specify the input, map the stream you want to the audio codec (acodec) pcam_s16e with 2 audio channels [-ac 2] to filename audio.wav

If you want to extract the 5.1 without downmixing (reccommended)

ffmpeg -i video.mkv -map 0:1 -acodec pcm_s16le -ac 6 audio.wav

The only thing we’ve changed is the number of audio channels. What would you change if you wanted to get a 24bit audio file?

PCM channel ordering

What if the channel ordering is messed up? You can hardwire the channel ordering like this:

ffmpeg -i video.mkv -map 0:1 -acodec pcm_s24le -ac 6 -af pan="5.1(side):c0=FL|c1=FR|c2=FC|c3=LFE|c4=SL|c5=SR" audio.wav

Extracting stems

If you want to extract the stems to individual files from the audio track you get above, try this;

ffmpeg -i yourAudioFile.wav -filter_complex "channelsplit=channel_layout=5.1[FL][FR][FC][LFE][BL][BR]" -map "[FL]" front_left.wav -map "[FR]" front_right.wav -map "[FC]" front_center.wav -map "[LFE]" lfe.wav -map "[BL]" back_left.wav -map "[BR]" back_right.wav

Using FFMPEG to extract a segment of your input file and export to something useful for your analysis:

Of course, you don’t really want to do this with a whole DVD and you may want to import the film with PCM audio into Reaper. So, decide which bit of the film you want to analyse. Get the start point in hours, minutes, seconds and find the duration and specify this -t. Specify the video codec for output, container format -f mov output movie name.

ffmpeg -i input.mkv -ss 00:01:45 -t 00:02:00 -vcodec h264 -acodec pcm_s24le -ac 6 -af pan="5.1(side):c0=FL|c1=FR|c2=FC|c3=LFE|c4=SL|c5=SR" -f mov output.mov

e.g.

ffmpeg -i bbss.mkv -ss 00:01:45 -t 00:00:30 -vcodec h264 -acodec pcm_s24le -ac 6 -af pan="5.1(side):c0=FL|c1=FR|c2=FC|c3=LFE|c4=SL|c5=SR" -f mov mySelection.mov

To get just the audio of your extract, perhaps as a downmixed stereo file to make some forms of analysis slightly simpler, you could try this

ffmpeg -i movieSource.mkv -ss 00:01:45 -t 00:00:30 -map 0:1 -acodec pcm_s24le -ac 2 stereoAudioDownMixOfSelection.wav

for a 5.1 version of the same

ffmpeg -i movieSource.mkv -ss 00:01:45 -t 00:00:30 -map 0:1 -acodec pcm_s24le -ac 6 -af pan="5.1(side):c0=FL|c1=FR|c2=FC|c3=LFE|c4=SL|c5=SR" surroundVersionOfSelection.wav

UPDATE

I have found that if you extract your video as .mov with hard wired 5.1 as above, Reaper doesn’t seem to like to import it nicely, even though it plays fine in media players. So run this on your extract and then import to Reaper and it seems to work

ffmpeg -i yourExtract.mov -vcodec copy -acodec pcm_s24le -ac 6 -af pan="5.1:c0=FL|c1=FR|c2=FC|c3=LFE|c4=SL|c5=SR" -f mov yourExtractToReaper.mov

Analysis of your audio

Check out SoX and install it on your machine (see above);

sox.sourceforge.net/

Look at the file formats that SoX can cope with;

sox.sourceforge.net/soxformat.html

Handy tutorial on generating spectrograms from SoX

jdesbonnet.blogspot.co.uk/2013/08/using-sox-spectrogram-tool-to-analyze.html

Try this in the command line

sox surroundVersionOfSelection.wav -n spectrogram -o spectrum.png

It might give you something like this, a spectrogram of each channel.

How about generating a spectrogram of Channel 3?

Extract the centre channel

sox surroundVersionOfSelection.wav centre.wav remix 3

Generate your spectrogram

sox centre.wav -n spectrogram -o centreSpectrogram.png

Want more detail from the key areas of the voice or extract? Try resampling. The command below will take your source audio, select 40 seconds starting at 20 seconds, resample the 48k to 6k, giving you a focus on the first 3k of the spectrum, it will do this to channel 3 and produce you a spectrogram of that 40 second clip:

sox audio.wav -n trim 20 40 rate 6k remix 3 spectrogram -o centreSpectrogram.png

You could explore some useful ways of exporting an image for every keyframe that you select in Reaper by exporting your markers as a csv or text file and using these indices to generate a still from the film and a spectrogram.

Here’s a way to extract a segment of audio that you want to concentrate on. It should take your surround audio file, generate a new file called Klangers.wav, trim 10 seconds at second 33 and give you only the centre channel. This is useful because it gives you the sound file of the same extract you’ve visualised.

sox audio.wav klangers.wav trim 33 10 remix 3 -n rate 5k spectrogram -o klangers.png

Extra/off-topic – using ‘for’ to do batch conversion

batch convert from flac to alac (apple lossless) and add image file, navigate to your folder of flacs and  punch this in

for f in *.flac; do ffmpeg -i "$f" -c:a alac "${f/%flac/m4a}"; done

batch add artwork with mp4 art. This is part of the mp4v2 package which you simply install with

brew install mp4v2

Then try this, which looks for all the m4a (apple lossless files in the direcotry, then adds the .jpg file in the same directory.

for f in *.m4a; do mp4art --add *.jpg "$f"; done

to join them both if conversion to ALAC was successful, use &&

for f in *.flac; do ffmpeg -i "$f" -c:a alac "${f/%flac/m4a}"; done && for f in *.m4a; do mp4art --add *.jpg "$f"; done

Links

Some useful links and starter tips for command-line processing

SoX

www.thegeekstuff.com/2009/05/sound-exchange-sox-15-examples-to-manipulate-audio-files/

FFMPEG

ffmpeg.org/
FFMPEG Audio RESAMPLER: ffmpeg.org/ffmpeg-resampler.html
Commands for all needs;
www.catswhocode.com/blog/19-ffmpeg-commands-for-all-needs
Batch Scripting, yeah!
www.gna-productions.com/tutos/video/how-to-use-ffmpeg-with-batch-scripts

Helpful indeed:

gist.github.com/protrolium/e0dbd4bb0f1a396fcb55

Useful too:

superuser.com/questions/538112/meaningful-thumbnails-for-a-video-using-ffmpeg

SPEAR

www.klingbeil.com/spear/

Sonic Visualiser

sonicvisualiser.org/