[FFmpeg-user] 5.1 AAC without lowpass on the LFE channel

Clay clay at 42streams.com
Thu Sep 15 23:27:27 EEST 2022


Is there a way to specify the LFE bitrate separately from the other
full-range channels?

Steven Ruppert via ffmpeg-user wrote on 9/15/22 16:24:
> On 9/12/22 09:33, Steven Ruppert via ffmpeg-user wrote:
>> I couldn't find any references whether that's inherent to the AAC 5.1
>> encoding, something that ffmpeg does, or inherent to the decoding
>> process. (I did decode my same test files using something that uses
>> Microsoft MediaFoundation and the LFE channel was still lowpassed).
>
> Turns out the AAC codec inherently limits the LFE bandwidth, so
> there's no way around it.
>
> The actual ISO/IEC 13818-7:2006(en) Standard costs a bunch of money to
> read as usual, but in the free glossary there is an entry:
>
> >low frequency enhancement ( LFE ) channel: limited bandwidth channel
> for low frequency audio effects in a multichannel system
>
> https://www.iso.org/obp/ui/#iso:std:iso-iec:13818:-7:ed-4:v1:en
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