AAC USAC Mps212 support

[Artem S. Tashkinov]

Here's a live xHE-AAC radio station:

​https://www.maxradio.ca/UHD/MaxRadio/48k/Max.m3u8

It actually worked with ffmpeg 6.1.2 albeit audio quality was horrible.

ffmpeg 7.1 just bails out:

Error decoding audio.
[ffmpeg/audio] aac: AAC USAC Mps212 is not implemented. Update your FFmpeg version to the newest one from Git. If the problem still occurs, it means that your file has a feature which has not been implemented.

ffmpeg 7.1 also fails to mux it:

Input #0, hls, from 'https://www.maxradio.ca/UHD/MaxRadio/48k/Max.m3u8':
  Duration: N/A, start: 4164154.700045, bitrate: 48 kb/s
  Program 0 
    Metadata:
      variant_bitrate : 0
  Stream #0:0(und): Audio: aac (xHE-AAC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 48 kb/s (default)
      Metadata:
        variant_bitrate : 0
        compatible_brands: isomiso6hlsfmp42
        handler_name    : StreamS Encoder
        vendor_id       : [0][0][0][0]
        major_brand     : mp42
        minor_version   : 0
        creation_time   : 2024-08-13T07:32:00.000000Z
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
[adts @ 0x11498300] MPEG-4 AOT 42 is not allowed in ADTS
[out#0/mpegts @ 0x1076a9c0] Could not write header (incorrect codec parameters ?): Invalid data found when processing input
Conversion failed!


ERROR: ffmpeg exited with code 183

A few more xHE-AAC streams: ​https://www.hiresaudio.online/max-radio-society/

Assigning to Lynne if that's OK. :-)

[Lynne]

Mps212 is MPEG-H surround, not xHE-AAC. It's not part of the base spec.

Not really a priority right now.

The MPEG-H spec is a different dimension of cursed.

[Artem S. Tashkinov]

Got it, but then why ffmpeg 6.1.2 is able to decode this stream while ffmpeg 7.1 fails?

Looks like an unintended regression to me :-)

[Lynne]

It was a coincidence. xHE-AAC uses the same scalefactor coding as regular AAC, which could be mistaken by a very robust AAC decoder as valid, and result in a semi-horrible sounding output, as the per-band volume levels would be similar.

Decoding codecs with clearly incompatible decoders is not and has not been supported.

[alexanderino]

Hi all,

the latest ffmpeg master [2025-09-07] fails spectacularly when attempting to decode a USAC + SBR + PS file. Please check this pastebin log (skipping is enabled, and this log is much shorter than the one when no skipping is performed): ​https://pastebin.com/vDc6bVKN

It's worth noting that music players using ffmpeg to decode USAC files find it impossible to play them without flaws.

Please let me know if anything is required.

Regards,

alexanderino

[Artem S. Tashkinov]

Replying to alexanderino:

Please let me know if anything is required.

Patches or funding :-)

[alexanderino]

Replying to Artem S. Tashkinov:

Patches or funding :-)

*cries*