Changes between Version 19 and Version 20 of Encode/AAC


Ignore:
Timestamp:
Oct 30, 2013, 9:49:59 PM (6 years ago)
Author:
llogan
Comment:

lbfdk-aac configure clarification; nits

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  • Encode/AAC

    v19 v20  
    1111== libfdk_aac ==#fdk_aac
    1212
    13 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 --enable-nonfree`. 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.
     13Fraunhofer 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.
    1414
    1515=== Constant Bit Rate (CBR) mode ===#fdk_cbr
     
    4141=== Variable Bit Rate (VBR) mode ===#fdk_vbr
    4242
    43 These settings target a ''quality'', rather than a specific ''bit rate''. 1 is lowest quality (though still pretty good) and 5 is highest quality. Test it out and use the lowest setting that works for you. This mode is not compatible with [[#fdk_he|AAC-HE]], but for AAC-LC (the default for ffmpeg, and most compatible [[http://en.wikipedia.org/wiki/Advanced_Audio_Coding#Modular_encoding|AAC profile]]) it should probably be preferred, since it allows the encoder greater flexibility to distribute bits as it sees fit: high-tempo, large dynamic range audio (like dubstep or rock music) requires more bits to encode then low-tempo, low dynamic range audio (like whalesong, or a recorded lecture - though there are special speech codecs that you should consider for the latter). Set the VBR level with the `-vbr` flag.
     43Target a ''quality'', rather than a specific ''bit rate''. 1 is lowest quality and 5 is highest quality. Test it out and use the lowest setting that works for you. This mode is not compatible with [[#fdk_he|AAC-HE]], but for AAC-LC (the default for ffmpeg, and most compatible [[http://en.wikipedia.org/wiki/Advanced_Audio_Coding#Modular_encoding|AAC profile]]) it should probably be preferred, since it allows the encoder greater flexibility to distribute bits as it sees fit. Set the VBR level with the `-vbr` flag.
    4444
    4545According to [[http://www.hydrogenaudio.org/forums/index.php?showtopic=95989|this hydrogenaudio post]], the VBR modes (on average, over a number of files) give the following bit rates per channel (so for stereo, double the bit rate; for 5.1 surround sound, multiply it by six):
     
    7575=== High-Efficiency AAC ===#fdk_he
    7676
    77 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).
     77This is a pair of AAC profiles tailored for low bit rates (version 1 and version 2). VBR mode is not compatible with [[#fdk_he|AAC-HE]] so a bitrate is declared. 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).
    7878
    7979Unfortunately, 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.
    8080
    81 The following examples are adapted from [[http://ubuntuforums.org/showpost.php?p=12421935&postcount=34|this Ubuntu Forums post]].
    8281
    8382==== AAC-HE version 1 ====