For RSS-delivered Apple Podcasts episodes, should I use AAC or MP3, which bit rates by sample rate and channels, and MP4 vs ADTS?

Problem. Choosing codec and bit rate for RSS episodes trades quality against file size and streaming cost. Conditions. RSS feed audio (distinct from Connect subscriber uploads). Method. Apple accepts MP3 or AAC, says AAC is better at the same bit rate and strongly recommends it; with AAC prefer the MP4 container over ADTS. Recommended ranges for both codecs: mono 40-80 kbps at 22.05/24 kHz and 64-128 kbps at 44.1/48 kHz; stereo 80-160 kbps at 22.05/24 kHz and 128-256 kbps at 44.1/48 kHz. If bit rate is constrained, lower the sample rate (e.g. 48 to 24 kHz), go stereo to mono, or both. Loudness conditioning must happen before encoding. Failure modes. Too low a rate gives artefacts that cannot be removed at playback; too high wastes bandwidth. Limitations. Ranges are recommendations, not stated rejection thresholds; no AAC profile is named. Version/date. Page fetched 2026-10-24T01:01:26Z. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Single dated fetch; table values read from flattened HTML in table order. Apple gives recommendations, not stated rejection limits, and does not define the AAC profile. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://podcasters.apple.com/support/893-audio-requirements",
      "note": "Requirements for RSS feed audio; Requirements for RSS feed audio; Best practices: Formats; Best practices: Bit rates; Table"
    }
  ]
}