Audio Quality

Muammar El Khatib edited this page May 24, 2017 · 18 revisions

Bitrates

In Mkchromecast you can modify the bitrate to stream using the -b or --bitrate options:

python mkchromecast.py -b 320

If you are using the system tray, there is an option in the Preferences menu.

In general, the higher the bitrates the better sound quality. Of course, this is not true in some cases. For instance, aac between 128-256k is already considered transparent (in other words, average listeners do not perceive any differences). Between mp3 and ogg, starting from a bitrate of 128k, ogg already delivers a better sound quality than 320k mp3.

The sound quality from the better to the "worse" lossy data compression formats:

aac > ogg > mp3.

You can use different audio formats provided you install ffmpeg or avconf as follows:

python mkchromecast.py --encoder-backend ffmpeg -c ogg

If you intend to use high bitrates for these lossy data compression audio formats, you should instead consider using flac or wav.

python mkchromecast.py --encoder-backend ffmpeg -c flac

Lossy formats

The MP3 audio format lossy data compression.

Audio quality improves with increasing bitrate:

  • 32 kbit/s – generally acceptable only for speech.
  • 96 kbit/s – generally used for speech or low-quality streaming.
  • 128 or 160 kbit/s – mid-range bitrate quality.
  • 192 kbit/s – medium quality bitrate.
  • 256 kbit/s – a commonly used high-quality bitrate.
  • 320 kbit/s – highest level supported by the MP3 standard. Used in Deezer premium subscription.
The OGG audio format lossy data compression.

OGG provides the same quality for a lower filesize compared to MP3

  • 45 kbit/s or 48 kbit/s
  • 64 kbit/s
  • 80 kbit/s - medium quality bitrate.
  • 96 kbit/s
  • 112 kbit/s
  • 128 kbit/s - High quality.
  • 160 kbit/s
  • 192 kbit/s
  • 224 kbit/s
  • 256 kbit/s
  • 320 kbit/s - Used in Spotify premium subscription.
  • 500 kbit/s
The AAC audio format lossy data compression.
  • 128 kbit/s - High quality, Stereo.
  • 256 kbit/s - Quality as good as CD. Used in Apple Music service.
  • 320 kbit/s - Used in Tidal high quality subscription.

Lossless formats

wav and flac are considered lossless formats. When using ffmpeg or avconv encoder backends, the option '-acodec pcm_s24le' assures 24-bit.

As for the bitrates, wav operates about 1411 kb/s, while flac does it at ~900 kb/s.

High audio resolution (24-bit/96kHz)

Mkchromecast lets you cast using 24-bit/96kHz high audio resolution. This is the maximum chromecast audio capability. The supported codecs are: wav and flac. In spite of the fact that aac can use 96000Hz sample rate, the bitrate corresponds to that of a lossy data compression format. Therefore, the following combinations can achieve this 24-bit/96kHz capability:

  • wav + 96000Hz sample rate.
  • flac + 96000Hz sample rate.

Reference: #11.

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