What is an MKA audiobook, and how do you play or convert one?

An .mka file is Matroska audio, the audio-only sibling of .mkv video. It’s a wrapper around audio in another format, usually MP3 for audiobooks. The fix is usually quick and lossless: copy the audio out into MP3 for MP3 inside, M4B for AAC inside, without re-encoding.

Who can play it

Player	Opens .mka?
VLC, mpv on the desktop	Yes
Many Android players	Yes
iPhone, iPad, Safari	No
Other browsers	Not reliably

The audio inside is sometimes AAC, Opus or FLAC rather than MP3. The wrapper can also carry chapter marks and cover art.

Step 1: find out what’s inside

The file name doesn’t tell you; the codec inside decides what you can do. With ffmpeg installed (it includes ffprobe):

ffprobe -v error -select_streams a:0 -show_entries stream=codec_name -of csv=p=0 "Book.mka"

It prints one word: mp3, aac, opus, flac and so on. MediaInfo shows the same as the audio track’s Format, if you’d rather click. To see the chapters:

ffprobe -v error -show_chapters "Book.mka"

Step 2: copy the audio out

MP3 inside: make an MP3. This copies the stream bit for bit and writes the chapters as ID3 chapter frames:

ffmpeg -i "Book.mka" -map 0:a:0 -c:a copy -map_chapters 0 -id3v2_version 3 "Book.mp3"

The audio plays everywhere, though not every player reads MP3 chapter frames.

AAC inside: make an M4B, the usual audiobook file:

ffmpeg -i "Book.mka" -map 0:a:0 -c:a copy -map_chapters 0 "Book.m4b"

Opus, FLAC or anything else: re-encode, or keep it. These can’t go into an MP3 as they are, and most audiobook players won’t play them in an M4B. Converting loses a little quality. For a spoken voice, AAC at 64 to 96 kbit/s is plenty:

ffmpeg -i "Book.mka" -map 0:a:0 -c:a aac -b:a 96k -map_chapters 0 "Book.m4b"

Or keep the .mka and use a player that opens it.

-map 0:a:0 takes only the first audio track, so it leaves out cover art stored as an attachment. A cover.jpg in the book’s folder covers that for most players. Keep the original until the new file plays through with chapters in the right places.

A whole folder at once

Run this inside the folder. It checks each .mka and makes the lossless copy where there is one (-n never overwrites an existing file):

for f in *.mka; do
  codec=$(ffprobe -v error -select_streams a:0 -show_entries stream=codec_name -of csv=p=0 "$f")
  case "$codec" in
    mp3) ffmpeg -nostdin -n -i "$f" -map 0:a:0 -c:a copy -map_chapters 0 -id3v2_version 3 "${f%.mka}.mp3" ;;
    aac) ffmpeg -nostdin -n -i "$f" -map 0:a:0 -c:a copy -map_chapters 0 "${f%.mka}.m4b" ;;
    *)   echo "Skipped $f ($codec): needs re-encoding" ;;
  esac
done

For a book in many parts, M4B vs MP3 compares the two results, and Why audiobook files play out of order covers numbering the parts.

How AudioSilo handles MKA

AudioSilo indexes .mka books. Its server uses ffmpeg (included in the Docker image) to make them play:

• MP3 inside plays everywhere from server 2.5.0: web player and the iOS and Android apps, downloads included, with the apps you already have. On an iPhone, app 2.5.0 plays them best and is needed for downloads. The server makes the copy above once per file, keeps it in its data folder and serves it in place of the .mka. Your files are never changed. MKA audiobooks now play in the iPhone and Android apps has the details.
• Other audio inside plays in the web player, converted to MP3 as it streams, and on an Android phone that can decode it. For the iPhone app, convert it as above.

If you convert in place, you needn’t delete the .mka straight away. AudioSilo leaves out an .mka with the same name as another audio file beside it (Book.mka next to Book.m4b), treating it as that file’s source. The docs list every format under Supported formats.