To convert DTS to AC3, you decode the DTS soundtrack and re-encode it as AC3 (Dolby Digital) while copying the video untouched. The free, open-source FFmpeg tool does this in one command, and it can keep the original DTS track alongside the new one. Check first whether you need to, though. If your player can decode DTS itself, or the file already carries an AC3 track, conversion only costs time and some quality. It earns its keep when a TV, soundbar or receiver accepts Dolby Digital but not DTS, especially over an optical cable.
The steps below were checked when FFmpeg’s download page listed release 9.0.2. The commands use long-standing FFmpeg options, but device format support changes with firmware updates, so check your own hardware’s current specifications before you convert a whole library.
When you need to convert DTS to AC3, and when you don’t
DTS and AC3 are both compressed surround formats. The problem is simply that some devices decode one and not the other, which is explained in more depth in why DTS or Dolby plays and the other is silent. Before converting anything, find your setup in this table.
| Your setup | Convert? | Better first move |
|---|---|---|
| The file already has a second track in AC3, AAC or stereo | No | Select that track in the player’s audio menu |
| A computer or player that decodes DTS, connected by HDMI to a receiver or an eARC soundbar | Usually no | Let the player decode DTS and send PCM |
| You only listen in stereo, on TV speakers or headphones | No | Let the player decode to stereo |
| A soundbar or receiver without DTS support, connected by optical, and you want 5.1 | Yes | Convert, and keep the original file |
| The TV’s own media app plays files from USB and the TV has no DTS decoder | Often yes | Convert, or play the file from a device that decodes DTS |
Why the cable decides so much
Where the decoding happens matters more than the format itself. Over HDMI, a player can decode DTS on its own and send the result as uncompressed audio, so the receiver never sees DTS at all. The HDMI Licensing Administrator’s eARC page says eARC supports “uncompressed 5.1 and 7.1,” which means an eARC soundbar can take decoded surround sound directly from the TV.
An optical cable is more limited. It carries 5.1 surround only as a compressed stream such as Dolby Digital or DTS, and uncompressed audio sent over optical arrives as stereo. So if your soundbar is on optical and does not understand DTS, you have two choices: accept stereo, or give it Dolby Digital. That second case is where converting DTS to AC3 is the right tool. The guide to a soundbar with no sound over optical covers the rest of that chain, and what to do when a TV has no optical output covers the other connection options.
What conversion costs you
Converting is not free, and it helps to know the trade-offs before you start.
- It is lossy to lossy. Standard DTS and AC3 both discard data to save space. Converting means decoding one compressed format and compressing again into another, so some detail is lost a second time. How noticeable that is depends on the source and your system, but it is never an improvement.
- Lossless tracks lose their advantage. DTS-HD Master Audio is lossless. Once converted to AC3, it is not.
- Extra channels are folded down. The IETF’s RFC 4184 states that “AC-3 can deliver up to 5.1 channels of audio.” A 7.1 source has to be mixed down to 5.1.
- There is a bitrate ceiling. The same RFC says “Data rates can vary between 32 kbps and 640 kbps, depending on the number of channels and the desired quality.” For a 5.1 conversion, using the top of that range keeps the second round of compression as gentle as the format allows.
This guide covers your own files that are not copy-protected. It does not cover discs or streams with copy protection.
Get the tools safely first
The search results for this topic are crowded with “free converter” download portals, bundled installers and online upload tools. You do not need any of them.
- Use FFmpeg from its official site. FFmpeg is a free, open-source command-line tool for converting audio and video. Its download page at ffmpeg.org states that “FFmpeg only provides source code,” and links to the ready-made builds it points Windows and Mac users to. Start from that page, not from a search result or a mirror.
- Skip codec packs. A codec pack helps a player decode formats. It does not convert a file, and it adds risk to your system for no gain here.
- Think twice about online converters. They require uploading your file to someone else’s server, often have size limits, and are not needed for a job FFmpeg does locally.
- Check graphical converters before trusting them. Many video converters re-encode the video as well as the audio. That is slow and lowers picture quality for a problem that sits only in the soundtrack. If you use one, look for an option to copy or pass through the video stream.
How to convert DTS to AC3 with FFmpeg
FFmpeg runs from a command window: Command Prompt or PowerShell on Windows, Terminal on a Mac. Run each command from the folder that holds your file, and replace input.mkv and output.mkv with your own file names.
Step 1: See which tracks the file contains
ffprobe -hide_banner input.mkv
The output lists every stream in the file with its type and format. A DTS soundtrack shows dts after Audio:, often followed by the variant, such as DTS-HD MA. Note how many audio tracks there are and how many channels the DTS track has.
Step 2, option A: Replace every audio track with AC3
ffmpeg -i input.mkv -map 0 -c copy -c:a ac3 -b:a 640k output.mkv
What each part does:
-map 0keeps every stream from the input: video, audio and subtitles.-c copycopies all streams without re-encoding them.-c:a ac3overrides that for audio only, encoding it as AC3.-b:a 640ksets the AC3 bitrate to the top of the format’s range.
This converts every audio track in the file, including any that were already fine. It is the simplest option, and your original file stays untouched as input.mkv.
Step 2, option B: Keep DTS and add AC3 as the first track
ffmpeg -i input.mkv -map 0:v -map 0:a:0 -map 0:a:0 -map 0:s? -c copy -c:a:0 ac3 -b:a:0 640k -disposition:a:1 0 output.mkv
This maps the first audio track twice. The first copy becomes the new AC3 track, and the second copy is the original DTS, left untouched. -map 0:s? brings along subtitles if the file has any. -disposition:a:1 0 clears the default flag from the DTS copy, so devices that pick the default track pick the AC3 one. This option keeps the best version for any future setup that does support DTS.
If the DTS track is 7.1
Because AC3 stops at 5.1, tell FFmpeg to produce six channels. In option A, add -ac 6 after -b:a 640k. In option B, add -ac:a:0 6 after -b:a:0 640k.
Step 3: Test on the device that needed it
Play the new file on the TV, soundbar or receiver that could not handle DTS. Check that the audio menu shows the AC3 track, that the device’s display or info screen reports Dolby Digital, and that dialogue stays in sync with the picture across the whole file. Keep the original until you are satisfied.
Converting a standalone .dts audio file
If you have a DTS audio file rather than a video, the command is shorter:
ffmpeg -i input.dts -c:a ac3 -b:a 640k output.ac3
The same channel rule applies: add -ac 6 if the source has more than six channels.
If the result is not what you expected
- Still silent on the device. The device may be choosing the DTS track. Use option A, or choose the AC3 track manually in the player’s audio menu.
- FFmpeg reports that a map matches no streams. A required stream is missing, for example
-map 0:son a file with no subtitles. Adding a question mark, as in-map 0:s?, makes that mapping optional. - The device plays AC3 in stereo only. Check the player or TV’s digital audio output setting. On many devices, a setting such as PCM decodes the track to stereo before it leaves the device, while passthrough or bitstream sends the AC3 as it is. The walkthrough for Fire Stick audio passthrough settings shows what that setting looks like on one common streaming device.
- Dialogue sounds quieter than on the original. Folding 7.1 to 5.1, or 5.1 to stereo on the device, changes how the channels are balanced. Try the file on another output before assuming the conversion itself failed.
FAQ
Does converting DTS to AC3 lose quality?
Yes, some. Both standard DTS and AC3 are lossy formats, so conversion decodes one and compresses the result again. Using 640 kbps, the top of the AC-3 range listed in RFC 4184, keeps that loss as small as the format allows. A lossless DTS-HD Master Audio track loses its lossless quality entirely.
What bitrate should I use when converting DTS to AC3?
RFC 4184 gives AC-3’s data rate range as 32 kbps to 640 kbps, depending on the number of channels and the desired quality. For a 5.1 conversion, 640 kbps is a sensible choice because it is the most the format carries.
Can I convert a 7.1 DTS-HD track to AC3?
Yes, but the result will be 5.1, because AC-3 can deliver up to 5.1 channels. Add -ac 6 to the FFmpeg command so the downmix to six channels is explicit.
Can I play DTS without converting it?
Often, yes. Select another audio track if the file has one, use a player that decodes DTS itself, or let a computer or streaming player decode DTS and send uncompressed audio over HDMI. Conversion is mainly for devices that need Dolby Digital, especially over optical.
Are online DTS to AC3 converters safe to use?
They require uploading your file to a third-party server and often limit file size. FFmpeg does the same job on your own computer, so there is no need to send your files anywhere.
