MKV DTS to AC3/AAC: How to Convert Audio

To convert an MKV file’s DTS audio track to AC3 or AAC, you need to re-encode just the audio stream using a tool like FFmpeg, HandBrake, or Avidemux, then remux it into the MKV container. This guide explains the process, the differences between AC3 and AAC, and the common pitfalls to avoid.

Why Convert DTS to AC3 or AAC?

DTS (Digital Theater Systems) is a high-quality surround sound codec often found on Blu-ray discs and in MKV rips. However, DTS is not universally supported by all devices. Many smart TVs, streaming sticks, game consoles, and soundbars can decode AC3 (Dolby Digital) or AAC (Advanced Audio Coding) but not DTS. Converting the audio track ensures your MKV file plays with sound on all your devices, or that the audio is compatible with a specific editing or streaming platform.

Understanding the Codecs: DTS, AC3, and AAC

Before converting, it helps to know what you’re dealing with:

• DTS: A lossy (or lossless in DTS-HD MA) surround sound format. Core DTS is typically 1.5 Mbps for 5.1 channels. It’s common on Blu-rays but less supported in consumer electronics.
• AC3 (Dolby Digital): A lossy codec, usually 384–640 kbps for 5.1 audio. It’s the standard for DVDs and broadcast TV, and nearly all devices support it.
• AAC: A more modern lossy codec, often used in iTunes, YouTube, and most streaming services. It offers better quality than AC3 at the same bitrate, but surround sound support is less universal (many devices only decode stereo AAC).

In short, AC3 is the safest choice for surround sound compatibility; AAC is better for file size and stereo playback.

What You Need: Software Options

You don’t need expensive software. Here are the most reliable free tools:

• FFmpeg: A command-line tool (powerful, scriptable, but requires learning terminal commands).
• HandBrake: A GUI tool that re-encodes video and audio. It can convert DTS to AC3 or AAC easily, but it re-encodes the video unless you use the “copyâ€� option.
• Avidemux: A simple editor that can copy video and convert audio only, making it fast (no video re-encode).
• MKVToolNix: Not a converter, but a remuxer. You can extract the DTS track, convert it with another tool, then mux it back.

Step-by-Step: Converting with FFmpeg (Command Line)

FFmpeg is the most flexible method. Here’s how to do it:

1. Install FFmpeg from the official website (ffmpeg.org) or a package manager.
2. Open a terminal/command prompt in the folder containing your MKV file.
3. To convert to AC3 (keeping video as is):
   ffmpeg -i input.mkv -c:v copy -c:a ac3 -b:a 640k output.mkv
4. To convert to AAC (stereo or 5.1):
   ffmpeg -i input.mkv -c:v copy -c:a aac -b:a 384k output.mkv
5. Wait for the process to finish. The video is copied, so it’s fast.

If you only want to convert the audio and keep the original DTS track as well, you can add -c:a:0 ac3 -c:a:1 copy to keep both.

Choosing Bitrate and Channels

Bitrate determines audio quality and file size. For 5.1 surround:

• AC3: Use 384–640 kbps. 640 kbps is the maximum for Blu-ray and gives excellent quality.
• AAC: Use 256–384 kbps for 5.1, or 128–192 kbps for stereo.

Check your source’s channel count with ffprobe (comes with FFmpeg): ffprobe input.mkv will show the audio streams. If the source is 5.1 and you convert to stereo AAC, you’ll lose the surround sound. If you want to downmix, FFmpeg can do that with -ac 2.

Common Mistakes and How to Avoid Them

People often run into these issues:

• Video re-encoding: If you use HandBrake without selecting “copyâ€� for video, it will re-encode video, taking hours and losing quality. Use Avidemux or FFmpeg with -c:v copy.
• Wrong channel mapping: If you downmix 5.1 to stereo, you may get quiet dialogue. Use the -ac 2 flag with proper downmix (FFmpeg does this automatically, but check the volume).
• Not matching the container: MKV supports AC3 and AAC, so that’s fine. But if you output to MP4, AC3 is not always supported (AAC is safer).
• Forgetting to check the output: Always play the output file to verify the audio track is present and syncs with video.

Frequently Asked Questions

Will converting DTS to AC3 lose quality?

Yes, because both are lossy codecs. You’re re-encoding from a lossy source, so there’s generational loss. However, at high bitrates (640 kbps AC3), the difference is barely audible to most listeners. If you have a DTS-HD MA track (lossless), you could keep it or convert to a lossless format like FLAC instead.

Can I convert DTS to AAC without re-encoding video?

Yes, using FFmpeg with -c:v copy as shown above. This copies the video stream untouched, so it’s fast and lossless for video.

Why does my TV not play DTS but plays AC3?

Many TV manufacturers don’t license DTS decoders to save costs. AC3 (Dolby Digital) is more widely licensed. Converting to AC3 solves this.

Is there a way to batch convert multiple MKV files?

Yes, with FFmpeg you can use a loop in your terminal. For example, in Windows Command Prompt: for %i in (*.mkv) do ffmpeg -i "%i" -c:v copy -c:a ac3 -b:a 640k "%~ni_ac3.mkv". In bash (Linux/macOS): for f in *.mkv; do ffmpeg -i "$f" -c:v copy -c:a ac3 -b:a 640k "${f%.mkv}_ac3.mkv"; done.

What’s the difference between AC3 and E-AC3?

E-AC3 (Enhanced AC-3) is an extension that supports higher bitrates and more channels (up to 7.1) and is used on some streaming services. It’s less compatible than AC3. Stick to AC3 for maximum compatibility.

Can I convert DTS to AAC in HandBrake?

Yes, HandBrake can do it, but you must set the video encoder to “H.264 (x264)� and the quality to “Constant Quality� with a high RF (e.g., 20) to avoid re-encoding video. Or, use the “Fast 1080p30� preset and then change the audio codec to AAC. But remember, HandBrake always re-encodes video unless you use the “Copy� option, which is only available in the CLI version.

Alternatives to Converting

If you don’t want to convert, you have a few options:

• Play with software that supports DTS: VLC, MPC-HC, and Kodi can decode DTS on any device.
• Use an external player: A media player like an NVIDIA Shield or a Blu-ray player can pass through DTS to a receiver.
• Extract and convert only the audio: Use MKVToolNix to extract the DTS track, convert it, and then mux it back. This gives you more control.

Converting is often the simplest path to universal compatibility, and with the right settings, you won’t notice a quality difference.

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