FFmpeg [aac @ ] Using a PCE to encode channel layout “5.1(side)”

If the source file signals a layout of 5.1(side) instead of 5.1, the AAC encoder will throw the error because the AAC spec only supports 5.1 (rear channels instead of side). The general cause of the problem is while transcoding to the AAC codec (Advanced Audio Coding) from various other high quality codecs such as AC3 (Dolby Digital/DD), E-AC-3 (Dolby Digital Plus/DDP/DD+), DTS, TrueHD (24-bit hd audio), it does not auto-select the standard 5.1 channel layout (called 5.1) if the original source has a channel layout of 5.1(side). While the AAC encoder may be able to automatically determine the amount of audio channels, FFmpeg has a hard time determining correct channel layout.