.ass files give incorrect MIME types

[rcombs]

Bug report

Bug description:

Advanced SubStation is a common subtitle format, with file usually having the extension .ass, and the .ass extension is not commonly used for AAC audio files. However, mimetypes currently gives audio/aac as the type for .ass files:

mimetypes.guess_type('test.ass') # -> ('audio/aac', None)

This appears to be due to this erroneous line:

cpython/Lib/mimetypes.py

Line 534 in 4fc82b6

'.ass' : 'audio/aac',

CPython versions tested on:

3.12

Operating systems tested on:

macOS

Linked PRs

• gh-120258: Correct MIME type for .ass files #120252

[ericvsmith]

Are you sure .ass isn't also used for AAC files? It's possible for a single extension to be used by more than one mime type. I'd be hesitant to change it.

[barneygale]

.ass is also used for Arnold scene descriptions: https://help.autodesk.com/view/ARNOL/ENU/?guid=arnold_user_guide_ac_scene_source_html

[rcombs]

I've been doing work in A/V across consumer and professional spaces for over a decade, from open-source to commercial software, and I've never seen .ass used as an extension for an AAC file; raw AAC bitstreams are fairly uncommon to begin with, and LOAS/LATM is essentially only seen in broadcast (where it's encapsulated in an MPEG-2 transport stream). Meanwhile, .ass is one of the most common text subtitle formats in current usage (along with WebVTT, TTML, and SRT).

[tirkarthi]

This was added in #24287 . As noted in the description this looks like an IANA recognized usage.

https://www.iana.org/assignments/media-types/audio/aac

File extension(s): .adts or .aac (ADTS), .loas or .ass (LATM/LOAS)

[picnixz]

Despite the popularity for .ass formats to be subtitles, I think it's better not to change the meaning of IANA usages. Considering #120252 (comment), I'm going to close this one (we really want to provide official mappings, not non-standard ones).