[FFmpeg-user] stereo downmix error aac HEv2
seandarcy2 at gmail.com
Sat Mar 15 03:45:03 CET 2014
On 03/14/2014 07:58 PM, Christian Ebert wrote:
> * Sean Darcy on Friday, March 14, 2014 at 19:10:30 -0400
>> More messing around, and it seems the HEv2 won't handle mono at all!
> Have a look at:
Thanks for the quick response. Very interesting.
So as I understand it HEv2 is HE + PS. And PS stands for Parametric
_Stereo_. I found:
https://tech.ebu.ch/docs/techreview/trev_305-moser.pdf which taught me
more than I ever wanted to know about AAC HE encoding.
So therefore HEv2 only makes sense with stereo.
We should put a note in the wiki not to use AAC-HEv2 with mono.
FWIW, here's the command line I'm now using to downmix to mono at a low
ffmpeg -i <input> -vn -c:a libfdk_aac \
-profile:a aac_he -b:a 48k -ac 1 -signaling implicit \
The output is shown as mono:
Output #0, ipod, to 'test-48kmono.m4a':
encoder : Lavf55.34.101
Stream #0:0: Audio: aac (libfdk_aac) (HE-AAC) (mp4a / 0x6134706D),
48000 Hz, mono, s16, 48 kb/s
but ffprobe shows the output file as stereo. mediainfo shows mono.
I'm assuming/hoping it's mono.
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