Support USAC / xHE-AAC

[Carl Eugen Hoyos]

xHE-AAC is currently not supported by FFmpeg, a sample stream is ​http://stream.radioh.no:443/rh.x16

$ ffmpeg -i rh.x16 
ffmpeg version N-95955-g12bbfc4cca Copyright (c) 2000-2019 the FFmpeg developers
  built with clang version 8.0.1 (tags/RELEASE_801/final 366581)
  configuration: --cc=clang --enable-gpl --enable-gnutls --enable-libxml2 --enable-libx264 --enable-libx265 --enable-libvpx --enable-libaom
  libavutil      56. 36.101 / 56. 36.101
  libavcodec     58. 64.101 / 58. 64.101
  libavformat    58. 35.101 / 58. 35.101
  libavdevice    58.  9.101 / 58.  9.101
  libavfilter     7. 67.100 /  7. 67.100
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
[aac_latm @ 0x3278800] Audio object type 42 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.                                                                                                 
[aac_latm @ 0x3278800] Audio object type 42 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.                                                                                                 

...

...

[aac_latm @ 0x3278800] Audio object type 42 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.
[aac_latm @ 0x3278800] Audio object type 42 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.
[loas @ 0x3276e40] decoding for stream 0 failed
[loas @ 0x3276e40] Could not find codec parameters for stream 0 (Audio: aac_latm, 0 channels, fltp): unspecified sample rate
Consider increasing the value for the 'analyzeduration' and 'probesize' options
Input #0, loas, from 'rh.x16':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Audio: aac_latm, 0 channels, fltp
At least one output file must be specified

[andrew46]

If it adds any weight to this enhancement request for FFmpeg to support USAC / xHE-AAC there is now (as of early 2020) an Open Source encoder available:

exhale
​https://gitlab.com/ecodis/exhale

This will doubtless result in more xHE-AAC sample files circulating in 'the wild' and a greater interest in encoding and decoding xHE-AAC (USAC) files...

[Elon Musk]

I deeply doubt that.

[Alex-Frst]

At least it makes sence to automaticaly switch to libfdk_aac decoder (if it's present) to decode xHE-AAC (USAC) now.

[Balling]

xHE-AAC is planned by Netflix. ​https://netflixtechblog.com/optimizing-the-aural-experience-on-android-devices-with-xhe-aac-c27714292a33

[Ronak Patel]

Hi, is there any update on when this support would be made available?

[Balling]

Replying to Ajaja:

At least it makes sence to automaticaly switch to libfdk_aac decoder (if it's present) to decode xHE-AAC (USAC) now.

libfdk_aac is not compatible (or more accurately does not allow redistribution) with ffmpeg's license (with GPL, not LGPL compilation), just like openssl. So it does not make sense to make it default. We cannot.

[rafael2k]

I added another sample here:
​http://abradig.org.br/xaac-sample/xaac-sample.mp4

I really think showing "Audio object type 42 is not implemented." is not a nice way to deal with the problem, as we most likely we will not have a xHE-AAC decoder in ffmpeg anytime soon... why not use the fdk-aac one?