Have you ever needed to extract the sound file from a downloaded video, such as videos from YouTube or other video sharing sites? In this post I will show how to separate the audio track from a video file (a process also known as “demuxing”).
Of late it seems that there is an increased interest in how to do this, which might have something to do with YouTube becoming the go-to destination for many people who want to look up music. Also, many download-from-YouTube programs are now adding the option to save straight to MP3.
Two sets of instructions will be presented for video files in FLV or MP4 formats, which are typically used in video sharing sites. Note that the tools covered here can also demux AVI, MOV and TS formats as well.
Some background info:
- This tutorial in two sections: (1) FLV videos, and (2) MP4 videos. FLV and MP4 are the two formats typically used by the majority of video sharing sites (e.g. normal YouTube vids are in FLV format, while HD YouTube vids are MP4s). Also note that M4V, MOV, and AVI formats can be demuxed using the same procedure as MP4s.
- Local files: I am assuming that your video is already downloaded to your hard drive.
- Video formats: This process does not work on FLV videos downloaded from Hulu. Although in fact the idea for this posting came after someone who read my “How to download from Hulu” article enquired about demuxing downloaded Hulu FLVs. See the bottom of this posting for more on my experience trying to demux Hulu videos.
- Downloading from video sharing sites: three of my favorites are TubeMaster++, xVideoServiceThief, and StreamTransport. These three present varying abilities to download both regular and encrypted videos. TubeMaster++ and xVideoThief can save the audio component separately from the get go, while StreamTransport is able to download from Hulu.
- Changing the audio format: if your resulting audio file is not in an audio format that you want, you can convert it to another format using any of the following apps: BonkEnc, Any Audio Converter, or MediaCoder Audio Edition.
- Increasing the volume: for the resulting audio file, can be done using a freeware program called MP3Gain.
(1) FLV format
The software used to do this is called ExtractFLV. This free program unpacks your video and audio tracks without re-encoding them, which means it is superfast and does not alter the original sound track.
Step#1: visit this site and download FLV Extract, then unzip. (Go here for a review of ExtractFLV previously published on Freewaregenius).
Step#2: run FLVExtract.exe; in the dialog, uncheck “Video” and “Timecodes” but keep “Audio” checked. (Note: if you would also like to extract the video component as its own seperate file, keep the “Video” box checked”)
Step#3: drag and drop you file or files to the FLVExtract dialog (see screenshot to the right).
You can drag files in batch if you like, and the program will process them serially.
Step#4: once processed, the audio files will appear in the same directory (typically in MP3 or AAC formats). The format of the audio depends on how the sound was 
encoded before it was packed into the FLV container; FLVExtract does not re-encode the audio but simply unpacks the audio file from the FLV container.If you would like to convert the sound file to a different audio format, see the “more notes” section below for some freeware conversion options.
(2) MP4 format
The software used to do this is called Yamb. It will extract the sound from MP4, M4V, AVI, and MOV file formats.
Step#1: you will need to download two files; visit this site and download the latest version of MP4Box and this site and download the latest version of Yamb. Unzip both folders to an appropriate location.
Step#2: if your video is in M4V format rename the extension to MP4.
Step#3: run Yamb.exe. Select “settings” from the left pane and click on the entry that appears: “Advanced Settings for Yamb and tools used by this GUI etc..”. In the new screen click on MP4Box in the left pane then point the “Location” field to the MP4Box executable you extracted in step1. For “Temp dir” you can simply point it to any directory of your choice or leave it blank. Click “next” when you’re done.
Step#4: click “editing” in the left pane, then in the right pane choose “click to extract streams from AVI/MP4/MOV/TS files.
Step#5: click on the folder icon to the right of the input field to select your video, select the audio track from the list underneath (typically the second one and typically in AAC format), then click the “Extract to MP4” radio button. Finally, change the output folder if you like then click next; the demuxing process will start and after a few seconds you’re done.
That’s it You’re done. If you want to convert the resulting file to another audio format or increase the volume, see the last bullet point in “some background info” above for a list of free software that can help you do this.
Demuxing FLV’s downloaded from Hulu – please share your experience.
I tried in vain to demux FLV videos downloaded from Hulu. I would appreciate your input if you were able to do it successfully.
- I downloaded a video from Hulu using StreamTransport, and added keyframe objects using FLVMDIGUI (as outlined here).
- ExtractFLV fails to recognize or extract the audio or video tracks.
- Surprisingly, neither Avidemux nor Movica would demux the video.
- I tried Gspot to get some info on the audio encoding used, without success.
Next I used MediaInfo, which showed that the audio format was AAC version 4 LC (see screenshot to the right).- More research lead me to AVInaptic, which seemed to extract the audio file. Instead of RAW format, I manually entered AAC for the file extension, but the file still would not play in any media player.
- I loaded the file into Audacity. It seemed that the audio was accelerated, yet my attempts to slow it down failed to render anything that sounded coherent.
- That’s when I gave up. Except I had a feeling that I may have made this too complicated, and that perhaps there was a much simpler approach that I totally missed.
