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, 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?