Capturing Youtube videos and extracting audio from video

Another HGFP (High Geekitude Factor Post)...

Capturing videos from Youtube and saving them to your hardrive is actually more straightforward than I thought it would be! Well, not quite as straightforward as right clicking on the video and selecting "Save as". If you right click on a Youtube video, all you get is the flash player context menu that has no save option. But it's still very easily doable.

In order to extract the video, you need to get a program that will do this for you. And the magical program is youtube.dl. The site has instructions on how to obtain it, install it and run it. For this post, I only share the third portion, which is using it. The good thing about this little piece of software is that you can use it on both Windows and Linux, so my Windows-running blogren should not feel left out.

For this post, I will use the following clip from Youtube of the opening credits for The Simpsons as an example:



To extract this video from the Youtube servers to your computer, you will need to issue the following command from wherever you installed the youtube.dl program. Again, this post assumes you are running Linux. You can reference the site linked to above for the appropriate commands to give in a Windows machine.

./youtube-dl -o file.flv http://youtube.com/watch?v=cZY7mSoZbCw

The only option needed is the -o which indicates what to name the output file, in this case, file.flv. Make sure to use the .flv extension, since you are extracting a flash video file. You then give the URL of the video as the argument. And off it goes.

Once done, you should have your file good to go and you can play it at will. In the unfortunate event you have a player that doesn't handle flash video files, then an extra step to convert the format to something else like mpeg will be necessary. Check my previous post for details on how to do this using MEncoder.

Next is the same clip that was extracted from Youtube.



And that's all there is to it. Something of note, before I move on. If you attempt to download a file and find that you need to be authenticated as a user, then you will have to give your youtube account username and password. The modified command would then be:

youtube-dl -u USERNAME -p PASSWORD -o file.flv http://youtube.com/watch?v=cZY7mSoZbCw

Just replace USERNAME and PASSWORD with your login info.

Moving on now to audio extraction. I will use audio from the video above for continuity's sake.

For audio extraction, I used mplayer. The command issued to get things going is:

mplayer -vc null -vo null -ao pcm file.flv

The options are:

• -vc: this indicates what video codec to use in decoding. The choice given is null, which means no decoding of the video signal will happen, since none is selected


• -vo: this indicates what video output drivers to use, i.e. what will be used to display the video. Again the choice given is null, meaning there will be no video output.


• -ao: this indicates what output audio drivers to use, meaning what will be used to play the sound. PCM has been selected as the driver to use, which is the uncompressed raw audio.

The last item is the file.flv which is the input to the application.

After a few seconds, you should have an audiodump.wav file generated from this command. You could use this as is, but if like me you'd rather have a compressed audio file occupying less space, then you need to issue the following command:

lame audiodump.wav file.mp3

This uses the lame application to convert from wav to mp3. Once again, you are not limited to lame. You can use any application that suits your fancy. In the command above, audiodump.wav is the input file, and file.mp3 is the output file. For this example, audiodump.wav is 6.9MB whereas file.mp3 is just 639KB.

The podcast below is of the audio extracted from the movie clip up above.


Incidentally, this is how I got the audio for the tv theme songs mix. For that mix, however, there was one extra step, which was combining of the different audio files into one big file. For that, I used audacity, available for Windows, Mac and Linux. That's the same application I used to generate these two mixes as well.

Apart from letting you combine files, this programme will let you edit sound files as well. I used it to cut different sections from the podcast below which I reproduced to give another example of audio extraction. This is from the choir video I digitized earlier.


Enjoy!