Podcast audio formats & processing

What audio codecs and formats does our platform support?

We accept almost any known audio file format as an input to publish a podcast episode. We also accept most video files as input, in which case we will use the first audio track in the video file.

What is the recommended upload format and quality ?

For typical podcast content (voice with some audio jingles or a background track) we recommend uploading 44.1kHz files compressed with AAC or OPUS at between 128 - 160kbps. At this compression level the quality should be nearly transparent to uncompressed originals. If you are uploading in MP3 format we recommend using a bitrate of 192kbps.

Our platform accepts variable bitrate encoded MP3, AAC and OPUS files and if this option is available we recommend encoding with any "high" quality VBR profile for these codecs.

We recommend against using WAV as an upload format due to it's massive size. We also accept FLAC lossless files, but seldom if ever find the additional quality to be worthwhile for podcast content.

How are files processed for delivery ?

Input files will always be converted to our standard set of formats and quality profiles for delivery to listeners and is never delivered "as-is".

• We distribute all files as stereo. When imported files are mono we duplicate the audio channel to create stereo output.

• We perform EBU R128 perceptual loudness normalisation at a Integrated Loudness target of -16 LUFS, a loudness range of 11 LUFS and True Peak limiting to -1.5 LUFS. This is the standard loudness level recommended by Apple and Google.

• Our "Low" quality profile downsamples to 32kHz sample rates.

Delivery profiles

All podcast episodes published on our platform are made available as 3 quality profiles to end users.

Different quality levels are employed to enable a better experience for users on slow (or expensive) internet connections while still allowing other users to receive high quality audio.

• The low quality profile enables extremely small file sizes, while still providing perfectly fine fidelity for consuming speech-centric content.
• The medium profile doubles the bitrate and produces a result that will satisfy the vast majority of listeners.
• The high profile doubles the bitrate again and mostly benefits users who listen on fast internet connections, in quiet environments using good sound equipment.

File formats

Supporting two different file formats (AAC & MP3) ensures wide platform support. While AAC is almost universally supported at this point, our player will intelligently detect when a browser does not support it and use the MP3 version.

AAC is used for the two smaller file-size profiles, because of it's massive improvement over MP3 at these lower bitrates. MP3 is used for the high quality one where the quality differences between AAC and MP3 are less noticeable.

Music

Our quality profiles are optimised for speech-centric content like podcasts, audiobooks and news broadcasts. Ambient music, intros, outros and other jingles will sound great, but our output formats are not ideal for delivering high quality music.