understanding fdk licence

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daaceking
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understanding fdk licence

Post by daaceking »

hi, here's a snippet from ffmpeg:-

Fraunhofer FDK AAC codec library. This is currently the highest-quality AAC encoder available with ffmpeg. Requires ffmpeg to be configured with --enable-libfdk_aac (and additionally --enable-nonfree if you're also using --enable-gpl). But beware, it defaults to a low-pass filter of around 14kHz. If you want to preserve higher frequencies, use -cutoff 18000. Adjust the number to the upper frequency limit you prefer.

does this mean that fdk has limitations in handbrake? i don't fully understand what this means.

thanks,
moneymatt4life
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Re: understanding fdk licence

Post by moneymatt4life »

it's lowpass filter won't go higher than 17kHz for 192-512kbps CBR UNLESS you specify it, in which case it still won't go above 20kHz, and this issue still carries over to handbrake. until handbrake can specify the lowpass filter and/or enable vbr, not much can be done unless mstorsjo fixes that in the source.
ONLY in vbr mode 5 will there be no lowpass filter (i think), but testing a 96kHz file, it does some other weird filtering i can't accurately explain so i'm not gonna try...
daaceking
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Re: understanding fdk licence

Post by daaceking »

ok, i'm in unchartered territory here so may say things which don't make sense but does handbrake use the full 20khz? i checked dolby digital's frequency set and that has a limit of 20khz too. so has handbrake made the necessary changes to make use of 20khz in every encode?
moneymatt4life
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Re: understanding fdk licence

Post by moneymatt4life »

not yet, no. although it is possible to go up to 22kHz in he-aac currently... if you like he-aac that is (^^',)
i personally would only allow fdkaac a lowpass of 20kHz for 256kpbs and higher... i'm not sure if i like 224kpbs with 20kHz, maybe it should be between 18-18.5kHz (19kz looks a little off compared to 18.5/19.5kHz)
daaceking
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Re: understanding fdk licence

Post by daaceking »

so is using fdk a bad choice? would it be better using a complete encoder like ac3 instead?
moneymatt4life
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Re: understanding fdk licence

Post by moneymatt4life »

well it's not bad per se, just has a technical quirk (^^',) which is why i see no reason to encode above 192kbps stereo/dpl2 with it as of right now... once vbr gets enabled i'll be using that for sure.

i've read that AC3 codec that handbrake uses is of lower quality compared to the offical AC3 codec... but it should be good enough at higher bitrates? i could be remembering wrong though...
daaceking
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Re: understanding fdk licence

Post by daaceking »

To be fair all the audio codecs say they're inferior except fdk which, like you said, has a technical quirk. :) my only concern is aac is more compatible than Dolby and certainly more so then DTS. I may opt in for a lower quality aac (without the quirk) or Dolby i guess :)
daaceking
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Re: understanding fdk licence

Post by daaceking »

hi, firstly, sorry for double posting but I have done further research on the matter.

so as I understand it, the issue is the treble area of a graphic equalizer seems to be the issue in laymans terms. according the source code in handbrake, there is no cutoff specified. so according to hydrogen audio & fdk-aac encoder documentation, it is specified by a table taking various calculations into consideration. Also, according to the documentation:-

"...they are based on numerious listening tests and careful tweaks to ensure the best overall encoding quality...."

so apparently, it's the realm of comparative/blind listening tests again? according to a website it said some people can't hear over 17khz anyway which seems to be the limit at which auto selection is done. so, there's nothing wrong with fdk? is that a fair statement? if anyone was to encode say 48khz 512kbps 5.1 audio to fdk-aac, the 17khz limit wuld be a moot point & not really an issue to do with lack of quality? :D
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Rodeo
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Re: understanding fdk licence

Post by Rodeo »

Just Get a Mac and use Apple's encoder ;)
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