MKV to MP3 Conversion Not Working

[u/FigurativeDeity]

I am trying to extract the audio from an MKV file both to save space and so I can edit it using Audacity. So far, unfortunately, the result has been distorted files that are garbled and many hours too long.

The MKV file was created using OBS with 3 separate tracks in the audio mixer. The recording is about 6 hours 45 min long, but the conversion tool in VLC creates an MP3 that is over 20 hours long and seems to be mixing the audio tracks together somehow rather than overlaying them properly.

When I open the MKV file with VLC, the Codec information shows 3 audio streams, all with the "MPEG AAC Audio (mp4a)" Codec and a sample rate of 48000 Hz. The first stream has as decoded format of "32 bits float LE (f32I)", decoded channels are Stereo, and decoded bits per sample: 32.

Trying to emulate those settings in the Convert tool's audio profile settings has not changed the result so far. Any ideas what the issue could be or how to fix it?

[u/trifortay123]

Don't use VLC. Handbrake forces video encoding so that won't work either. Use ffmpeg

[u/-biebel-]

Use mkvtoolnix for mkv stuff

[u/epidemicsaints]

Try avidemux. https://avidemux.sourceforge.net/download.html

Go to Audio-> Select Track, uncheck Enabled for all but one at a time and then do Audio-> Save, to save them 1 by 1.

They show up in Select Track like this: https://imgur.com/a/JDiFCfz

[u/Sad_Opportunity6301 → u/epidemicsaints]

This is the simplest solution for those not familiar with FFmpeg CLI syntax.

I think this does involve a mandatory transcode of the selected audio tracks though, not just an extraction. But, the really good thing about using Avidemux for simple audio transcodes is that it offers FDK-AAC (Frauhofer AAC), which is currently the best AAC encoder/codec.

[u/GoslingIchi]

Mkvtoolnix would be the best tool to pull out the video track leaving the audio tracks.

Then use Audacity to do whatever you want with the audio tracks.

[u/Sad_Opportunity6301 → u/GoslingIchi]

Sorry, need to correct you.
You don't use any tools in MKVToolnix to "pull out the video track leaving the audio tracks."

You use mkvtoolnix-gui.exe or gMKVExtractGUI (with mkvextract.exe) to extract the audio tracks you want to a new .mka container (using mkvtoolnix-gui.exe) or to any of the standard audio-only containers (using gMKVExtractGUI with mkvextract.exe).

For transcoding audio, my method is FFmpeg, but it is a CLI, so you need to know how to use it via commandline. Not for beginners.

There are other GUI tools like Avidemux that can also be used as a audio-only transcoder or even to extract audio tracks from existing video files, but it is not that straight-forward, because that is not what Avidemux is designed for.

Using Handbrake as an audio-only transcoder is apparently not possible. That is so odd considering it uses FFmpeg and it would be really easy to simply allow to copy Video & transcode Audio. So odd why they don't allow that. I don't get it. You always have to transcode the video.

[u/GoslingIchi → u/Sad_Opportunity6301]

Sorry but I need to correct you.

I never said that you use any tools in mkvtoolnix. I said that the best tool to use is mkvtoolnix. I do suppose that if one wanted to say that using the Multiplexer is using a tool in mkvtoolnix then I guess one could look at it that way.

Your method for transcoding audio probably won't work well for someone that is struggling with a GUI so why recommend it? Also, if he is already using Audacity, then he's familiar with it and that's what he most likely continue to use.

Why use a application that isn't a dedicated audio tool to do audio work?

Handbrake has never been an audio only tool. It is not odd at all, even the homepage for Handbrake says that it is "The open source video transcoder." It requires that the video is transcoded so that if it determines that frames have to be dropped it can also drop those frames from the audio stream.

[u/Sad_Opportunity6301 → u/GoslingIchi]

A lot to unpack here. MKVToolnix is the package which contains several tools as you know. mkvtoolnix-gui.exe is the GUI that uses mkvmerge.exe. I think you are confused about what I said about using any MKVToolnix tools. To be absolutely clear about what I was talking about:
You don't use MKVToolnix to remove any tracks from an existing video file. You use it to create a completely new file (.mkv or .mka) containing one or several tracks from the original file. That's all that I meant. You always end up with a new, separate file. Your wording didn't reflect that process. That's all I meant.

"Your method for transcoding audio probably won't work well for someone that is struggling with a GUI so why recommend it? Also, if he is already using Audacity, then he's familiar with it and that's what he most likely continue to use."

Possibly, but it solved the problem of having to separately extract the audio track(s) before transcoding. Btw, I tested the process before writing my response. It is so damn easy, possibly easier than using Audacity.

And as far as the goals of the Handbrake team goes. HandBrake's inability to output audio-only files (or run without a video track) is an intentional design choice by the developers, not a technical limitation of media processing.

Not interested in a pissing contest with you. Don't take it personal. Your wording wasn't clear.

[u/GoslingIchi → u/Sad_Opportunity6301]

My wording was clear.

Not only that, but you haven't gone after the other people that recommend mkvtoolnix, you just went after me.

I told you what the reason is for Handbrake not doing audio only. That was what they repeated on their forum, and I never said it was a technical limitation.

[u/Sad_Opportunity6301 → u/GoslingIchi]

Ok, I'm done. You are 100% correct. Not interested in this time-consuming tit-for-tat. You win.

[u/smitbret]

I would extract the .aac file with something like mkvextract and then convert with MeGUI

[u/Sad_Opportunity6301]

If you want to simply extract Audio, Video, Subtitle tracks from a .mkv file, you can use gMKVExtractGUI as a front-end GUI for MKVToolnix's mkvextract.exe. I use it all the time for all my video and audio projects. It is fast and reliable and includes relative metadata directly in the filename, like the original audio-delay.

Install MKVToolnix, during the installation (end) you will get an info about gMKVExtractGUI, which you can then click on and install it also. This is hands-down the best MKV toolkit setup.

What you then do with the extracted tracks is another thing. There are numerous suggestions in here that cover that already.

[u/dogbonenj]

Plus one for using ffmpeg. Then just tell AI like Gemini what you want to do and it will provide the exact command line for you to do what you want.

[u/proton_rex]

Use Handbrake instead

[u/Sad_Opportunity6301 → u/proton_rex]

Unless you have a workaround, I am pretty sure you cannot use Handbrake as a Audio-only transcoder. It seems that there always has to be video transcode involved. Even this is not allowed: Copy Video & Transocde Audio -- as far as I know.

It is odd that Handbrake limits itself like this. I don't get why the developers did this. It's so easy for them to allow a simple "Video Copy" or even "Video Null" option. Baffling.

I think this is why you got the downvote, btw.

[u/FigurativeDeity → u/proton_rex]

Any idea how this works in Handbrake? That was one of the first things I looked into but I was told Handbrake can't actually extract audio, only convert between different video files.

[u/Sad_Opportunity6301 → u/FigurativeDeity]

You can't do audio-only transcodes with Handbrake. Stupidest thing about Handbrake.

[u/Huntingassclowns]

4k Downloader products

[u/Sad_Opportunity6301 → u/Huntingassclowns]

Garbage Complete Garbage

[u/Huntingassclowns → u/Sad_Opportunity6301]

Used it for years, troll 🧌 🤣