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計算の仕組み

Two things are computed. The recommended window intersects a format range with your listening context: the low end is the larger of the format minimum and 0.7 × the audience minimum, the high end the smaller of the format maximum and 1.2 × the audience maximum. File size then uses the midpoint of that window, as (bitrate ÷ 8) × minutes × 60 ÷ 1024 megabytes, so 128 kbps for an hour is about 56 MB. The table repeats that size math for five durations.

Topic / format moves the answer most: Interview, the default, targets 35–65 minutes where Daily news / brief targets 5–12. Audience type then clips that window, with Commute (20–40 min), Workout (30–45 min) or Deep listen (60–120 min). Ad load changes nothing about the recommendation; it only subtracts 1.5, 3 or 6 minutes for Light, Medium and Heavy to show content time. Encoding bitrate touches file size alone, and 64 kbps AAC speech halves the megabytes of the 128 kbps default.

The ranges are baked-in editorial rules of thumb, not measurements of your own retention data, and nothing about your show's depth or pacing is modelled. Size assumes constant bitrate, so VBR encodes, artwork and chapter tags shift the real file by a few percent. Pick a mismatched pair, Daily news / brief with Deep listen for instance, and the two clamps cross, so the window prints backwards as 42–12 min. Read that as a contradiction rather than a recommendation.

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