Changes between Version 43 and Version 44 of Encode/AAC


Ignore:
Timestamp:
Jan 30, 2016, 7:06:02 AM (11 years ago)
Author:
Timothy Gu
Comment:

It's HE-AAC, not AAC-HE

Legend:

Unmodified
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  • Encode/AAC

    v43 v44  
    55[[http://en.wikipedia.org/wiki/Advanced_Audio_Coding|Advanced Audio Coding (AAC)]] is the successor format to MP3, and is defined in MPEG-4 part 3 (ISO/IEC 14496-3). It is often used within an MP4 container format; for music the .m4a extension is customarily used. The second-most common use is within MKV (Matroska) files because it has better support for embedded text-based soft subtitles than MP4. The examples in this guide will use the extensions MP4 and M4A.
    66
    7 FFmpeg can support three AAC-LC encoders (`aac`, `libfaac`, `libfdk_aac`) and two AAC-HE encoders (`libaacplus` and `libfdk_aac`). The licenses of `libaacplus`, `libfaac`, and `libfdk_aac` are not compatible with the GPL, so the GPL does not permit distribution of binaries containing code licensed under these licenses when GPL-licensed code is also included. Therefore these encoders have been designated as "non-free", and you cannot download a pre-built ffmpeg that supports them. This can be resolved by [[CompilationGuide|compiling ffmpeg]] yourself.
     7FFmpeg can support three AAC-LC encoders (`aac`, `libfaac`, `libfdk_aac`) and one HE-AAC(v1/2) encoder (`libfdk_aac`). The licenses of `libfaac` and `libfdk_aac` are not compatible with the GPL, so the GPL does not permit distribution of binaries containing code licensed under these licenses when GPL-licensed code is also included. Therefore these encoders have been designated as "non-free", and you cannot download a pre-built ffmpeg that supports them. This can be resolved by [[CompilationGuide|compiling ffmpeg]] yourself.
    88
    99See also [[Encode/HighQualityAudio]] for general guidelines on FFmpeg audio encoding (which also includes a comparison of which AAC encoder is best quality).
    … …  
    8383=== High-Efficiency AAC ===#fdk_he
    8484
    85 This is a pair of AAC profiles tailored for low bit rates (version 1 and version 2). AAC-HE version 1 is suited for bit rates below 64kb/s (for stereo audio) down to about 48 kb/s, while AAC-HE version 2 is suited for bit rates as low as 32 kb/s (again, for stereo).
    86 
    87 NOTE: AAC-HE version 2 only handles stereo. If you have mono, or want to down-mix to mono, use AAC-HE version 1.
    88 
    89 Unfortunately, many devices that can play AAC-LC (the default profile for `libfdk_aac`) simply cannot play either version of AAC-HE, so this is not recommended for surround sound audio, which normally needs to be compatible with such hardware players. If you are only going to play it on your computer, or you are sure that your hardware player supports AAC-HE, you can aim for a bit rate of 160kb/s for version 1, or 128kb/s for version 2. As always, experiment to see what works for your ears.
    90 
    91 
    92 ==== AAC-HE version 1 ====
     85This is a pair of AAC profiles tailored for low bit rates (version 1 and version 2). HE-AAC version 1 is suited for bit rates below 64kb/s (for stereo audio) down to about 48 kb/s, while HE-AAC version 2 is suited for bit rates as low as 32 kb/s (again, for stereo).
     86
     87NOTE: HE-AAC version 2 only handles stereo. If you have mono, or want to down-mix to mono, use HE-AAC version 1.
     88
     89Unfortunately, many devices that can play AAC-LC (the default profile for `libfdk_aac`) simply cannot play either version of HE-AAC, so this is not recommended for surround sound audio, which normally needs to be compatible with such hardware players. If you are only going to play it on your computer, or you are sure that your hardware player supports HE-AAC, you can aim for a bit rate of 160kb/s for version 1, or 128kb/s for version 2. As always, experiment to see what works for your ears.
     90
     91
     92==== HE-AAC version 1 ====
    9393
    9494{{{
    … …  
    9696}}}
    9797
    98 ==== AAC-HE version 2 ====
     98==== HE-AAC version 2 ====
    9999
    100100{{{
    … …  
    184184For AAC-LC the likely answer is: `libfdk_aac` > Native FFmpeg AAC encoder (`aac`) > `libfaac`.
    185185
    186 === Should I use AAC-LC or AAC-HE? ===
    187 
    188 If you require a low audio bitrate, such as ≤ 32kbs/channel, then AAC-HE would be worth considering if your player or device can support AAC-HE decoding. Anything higher may benefit more from AAC-LC due to less processing. If in doubt use AAC-LC. All players supporting AAC-HE also support AAC-LC.
     186=== Should I use AAC-LC or HE-AAC? ===
     187
     188If you require a low audio bitrate, such as ≤ 32kbs/channel, then HE-AAC would be worth considering if your player or device can support HE-AAC decoding. Anything higher may benefit more from AAC-LC due to less processing. If in doubt use AAC-LC. All players supporting HE-AAC also support AAC-LC.
    189189
    190190== Also See ==
    … …  
    195195{{{#!comment
    196196todo:
    197 Find out if libfdk_aac and libaacplus can be installed/supported at the same time. I can't remember. If not then add error(s) and any trac ticket # to FAQ and/or each encoder's section.
    198 
    199197List available metadata options for the MP4 container.
    200198