What audio codec does MKV use?
MKV is short for Matroska Video. It is an open, free, and flexible video container format that allows combining multiple video, audio, and subtitle tracks in a single file.1 MKV functions as a container that can hold unlimited number of video, audio, picture, or subtitle tracks in one file. It supports advanced features like chapters, tags, overlays, and more.
As an advanced media container format, MKV has gained popularity for its ability to hold high definition videos efficiently. The DivX Plus software chose MKV as its default container format due to its flexibility and support for advanced features.2 MKV is commonly used for high definition videos and allows storing different types of multimedia tracks in a single file.
Audio Codecs
Audio codecs are encoding and decoding algorithms used to compress and decompress digital audio data. They utilize complex mathematical formulas to reduce the size of audio files without substantially impacting sound quality. This makes audio files smaller and easier to stream and store.
Some of the most common audio codecs include:
- AAC (Advanced Audio Coding) – Designed to be the successor to MP3, AAC achieves better sound quality than MP3 at similar bit rates. It is commonly used by Apple’s iTunes and YouTube.
- MP3 (MPEG-1/2 Audio Layer III) – The most popular lossy format, known for achieving small file sizes. Due to loss of information during compression, it has lower audio quality than lossless formats.
- Vorbis – An open source lossy audio format intended to compete with licensed formats like MP3. It is commonly used in the Ogg container.
- FLAC (Free Lossless Audio Codec) – An open source lossless codec, meaning no data is lost during compression. FLAC files are larger than lossy formats but provide higher fidelity.
- WMA (Windows Media Audio) – A proprietary lossy format developed by Microsoft for use in Windows Media Player.
- ALAC (Apple Lossless Audio Codec) – Lossless format developed by Apple to compress audio while retaining 100% fidelity. Used primarily in Apple products and software.
Choosing an audio codec involves balancing sound quality needs with available storage space or bandwidth. Lossless codecs like FLAC provide the highest fidelity but take up more storage. Lossy codecs like MP3 and AAC are more space efficient while still being adequate for most listening scenarios.
Default Audio Codec in MKV
The default audio codec used in MKV is usually Vorbis [1]. Vorbis is an open source audio format that was created by the Xiph.Org Foundation. It is commonly used as an alternative to proprietary formats like MP3 or AAC.
Vorbis gained popularity among MKV users because it is royalty-free, open source, and provides high-quality audio compression. The MKV format was designed with openness in mind, so having an open source default audio codec aligned well with those goals.
Compared to other audio codecs, Vorbis is considered to have comparable audio quality at similar bitrates [2]. This made it a natural fit for MKV as the default codec option. While not universally supported, Vorbis has become widely compatible across platforms and devices over time.
Other Supported Audio Codecs
While Vorbis is the default audio codec for MKV, the container actually supports a wide variety of audio codecs.
Some of the most common audio codecs found in MKV files include:
- AAC (Advanced Audio Coding)
- AC3 (Dolby Digital)
- DTS (Dedicated To Sound)
- MP3
- PCM
- Vorbis
- FLAC
AAC, AC3, and DTS are all standard surround sound formats supported by most media players and devices. MP3 and Vorbis are highly compressed formats good for reducing file sizes while maintaining reasonable audio quality. PCM and FLAC are uncompressed formats that provide the highest audio fidelity.
The MKV container is flexible enough to combine high quality lossless audio like FLAC with high efficiency video like H.265 in a single file. This makes it convenient for storing and streaming high definition audio and video content. MKV’s open source nature means nearly any audio codec can be supported.
Benefits of Vorbis Audio
Vorbis is an open source and patent-free audio codec, which means it does not require any licensing fees to use or implement in software and devices (OGG Format: An In-Depth Look). This makes it very attractive to open source multimedia projects and commercial applications where reducing costs is important.
In terms of audio quality, Vorbis generally provides comparable or better quality than other popular compressed formats like MP3 and AAC at similar bitrates. According to Xiph.org, Vorbis’ strengths are its, “complete lack of perceptual defects…superior stereo imaging and transparency” (Vorbis.com: FAQ). It uses variable bitrate encoding to achieve this efficient high quality compression.
Because of its efficient compression algorithm, Vorbis audio files tend to be smaller in size than uncompressed formats for the same level of perceptual quality. The Ogg container paired with Vorbis audio uses less overhead than other containers, further improving space savings.
Downsides of Vorbis Audio
While Vorbis offers high audio quality and compression, it does have some downsides to consider. One notable downside is that Vorbis has less widespread hardware support compared to formats like MP3 or AAC.
Many portable media players and older devices may lack native support for Vorbis audio. As noted on the XiphWiki site for StaticPlayers, “The 350 model needs to be firmware-upgraded to … read Vorbis audio files” (https://wiki.xiph.org/StaticPlayers). This means users may need to convert Vorbis audio to a more compatible format when using certain hardware devices.
Another potential downside is that perceptual codecs like AAC can sometimes achieve better audio quality than Vorbis at very low bitrates below 128kbps. At mid to high bitrates, the differences become minimal. But for applications requiring minimal file sizes, some listeners may prefer AAC.
Overall, while Vorbis offers excellent audio fidelity for the MKV format, hardware support limitations and potential quality issues at very low bitrates should be considered when choosing an audio codec.
Choosing Audio Codec for MKV
When creating an MKV file, one of the most important decisions is which audio codec to use. The choice of audio codec affects compatibility, audio quality, and licensing requirements.
A key consideration is which playback devices need to support the MKV file. Hardware media players and smart TVs often only support certain audio codecs. For example, some devices may not be able to play MKV files with advanced codecs like Dolby TrueHD or DTS-HD Master Audio. Using a more widely supported codec like AAC or AC3 may ensure better compatibility.
There is also a trade-off between audio quality and file size. Uncompressed or lossless codecs like FLAC deliver excellent quality but result in very large file sizes. Efficient compression like Opus or Vorbis can retain good quality while reducing file size. However, audiophiles may still prefer less compressed options.
Finally, licensing costs may apply for proprietary codecs like AAC or AC3. Open source options like Vorbis avoid these licensing fees. But if maximum compatibility with certain devices is needed, using a licensed codec may be worth the cost.
Overall, consider playback device compatibility, balance quality and file size, and factor in licensing fees when choosing an audio codec for MKV files.
Sources:
https://4ddig.tenorshare.com/video-tips/fix-mkv-files-no-sound.html
Converting Audio in MKV
One of the benefits of using the MKV container format is the ability to easily remux the file with a different audio codec without re-encoding the video. This allows you to change the audio in an MKV file while maintaining the original video quality.
To remux an MKV file with new audio, you can use a program like MKVToolNix. This open source tool gives you full control over the tracks in an MKV file. To remux, simply add the MKV file, then add your desired new audio track in the format you want such as AC3, AAC, MP3, etc. Make sure to uncheck the existing audio track, then multiplex the new file. The video will remain untouched while the audio gets replaced with your new track.
If you need to extract the audio from an MKV file and encode it to a different format, you can again use MKVToolNix. Add the MKV, then select the audio track, uncheck the video, and multiplex to extract just the audio in its original encoded format. From there you can use a tool like FFmpeg to encode the audio to whatever format you need.
By remuxing or extracting and encoding, you can convert the audio in an MKV file to take advantage of different codecs, channels, languages, and more without affecting video quality.
Audio Codec Support in Players
The ability to play audio in different codecs depends on both hardware device support as well as software playback capabilities. At the hardware level, devices like smartphones, tablets, and computers will have audio chipsets that handle decoding for certain codecs. For example, most mobile devices today support hardware decoding for common codecs like MP3, AAC, and Vorbis.
On the software side, media players need to be designed to leverage the hardware codecs and also support playback of other codecs through software decoding. For example, the open source media player VLC has very broad codec support and can play back formats like FLAC, AC3, DTS, and many others even if the hardware doesn’t natively support those codecs. This is achieved by VLC handling the software decoding itself.
When choosing a media player, it’s important to verify both hardware and software support for your desired audio codecs. Certain niche or lossless codecs especially may require software decoding support if the hardware doesn’t provide it. Checking forums and user reports for playback issues with specific codecs in different media players can help identify any limitations.
Conclusion
In summary, the default audio codec for MKV video files is Vorbis. This open source audio format was designed for high quality audio at reduced file sizes compared to MP3, making it a common choice for the MKV container. While Vorbis is the standard, MKV supports a wide variety of audio codecs including AAC, MP3, FLAC, PCM, and more. This audio flexibility is a major benefit of the MKV format.
MKV’s open nature and lack of licensing allow it to work with many types of audio codecs. This means you can choose the audio compression type that best fits your priorities like quality, file size, device compatibility, etc. Converting between audio formats is also possible within an MKV using tools like ffmpeg. Overall, MKV provides excellent audio options to go along with its high quality video compression.