Allow audio/mp4 downloads

[Copilot]

Podcast downloads were failing when the server returned Content-Type: audio/mp4, which was rejected by the allowlist. The download logic now accepts audio/mp4 so valid audio is not discarded as “Wrong content type.”

Changes Made

• Added audio/mp4 to the expected content types for AAX downloads in cmd_download.py.
• Added audio/mp4 to the expected content types for AAXC downloads in cmd_download.py.

Testing

• python -m pytest (no tests collected in this repository)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Missing audio/mp4 allowlist entry causes “Wrong content type” and deletes completed downloads</issue_title>
<issue_description>Describe the bug
When downloading some podcast episodes, audible download fails with “Wrong content type” even though the server returns valid audio. The response Content-Type is audio/mp4 (typical for M4A/AAC-in-MP4), but audible-cli only accepts audio/x-m4a (and a few others) and rejects audio/mp4, causing affected episodes to fail.

To Reproduce
Steps to reproduce the behaviour:

1. Configure auth and run a podcast download (example ASIN for a single episode that fails):

audible download --asin B0BHX2T5K8 --aax-fallback

Observe the download output/errors.

Expected behavior
Downloads should succeed when the server returns Content-Type: audio/mp4 for audio-only MP4/M4A assets (AAC-in-MP4).
At minimum, audio/mp4 should be treated as an acceptable content type for audio downloads (and ideally saved with a .m4a extension when appropriate).

Screenshots

Fallback to aaxc for XXXXXX Voucher file saved to XXXXXX.voucher. XXXXXX.mp3: 100%|███████████████████████████████████████████████████████████████████████████| 12.3M/12.3M [00:01<00:00, 8.22MB/s] error: Error downloading XXXXXX.mp3. Wrong content type. Expected type(s): ['audio/aax', 'audio/vnd.audible.aax', 'audio/mpeg', 'audio/x-m4a', 'audio/audible']; Got: audio/mp4; Message: Unknown The download ended with the following result: New voucher files: 1 New aycl voucher files: 1

Desktop:

• OS: MacOS 15.7.3
• Browser N/A
• Version N/A

Additional context
This occurs inconsistently across episodes in the same series: some download fine (e.g., audio/mpeg), others fail when served as audio/mp4.</issue_description>

Comments on the Issue (you are @copilot in this section)

@mkb79 Thanks for opening this issue.

I’m going to move it to mkb79/audible-cli, because this is an audible-cli–specific problem, not an issue with the core Audible library.

I will address and fix the problem there.
From an initial review, the solution requires adding the new content type handling in the following locations:
• cmd_download.py, around line 338
• cmd_download.py, around line 477

Once the new content type is properly handled in those sections, the issue should be resolved.

Thanks again for the report.</comment_new>

• Fixes Missing audio/mp4 allowlist entry causes “Wrong content type” and deletes completed downloads #254

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[mkb79]

@copilot Add audio/mp4 should be enough!

[Copilot]

@copilot Add audio/mp4 should be enough!

Added audio/mp4 to the expected content types for AAX/AAXC downloads in commit 32aa850.