Changes between Version 22 and Version 23 of Encode/AAC


Ignore:
Timestamp:
Dec 5, 2013, 2:34:35 PM (13 years ago)
Author:
Kamedo2
Comment:

Stress that VBR encoding is experimantal.

Legend:

Unmodified
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  • Encode/AAC

    v22 v23  
    4141=== Variable Bit Rate (VBR) mode ===#fdk_vbr
    4242
    43 Target 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.
     43VBR encoding in libfdk-aac is '''experimental''' and only works with some parameter combinations. Target a ''quality'', rather than a specific ''bit rate''. 1 is lowest quality and 5 is highest quality. This mode is not compatible with [[#fdk_he|AAC-HE]]. 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):
    … …  
    9898The native FFmpeg AAC encoder is included with ffmpeg and is does not require an external library like the other AAC encoders described here. Note that you will not get as good results as with `libfdk_aac`. This is considered an experimental encoder, so `-strict experimental` or `-strict -2` is required.
    9999
    100 ==== Example using `-q:a` ====
    101 
    102 {{{
    103 ffmpeg -i input.wav -strict experimental -c:a aac -q:a 6 output.m4a
    104 }}}
    105 
    106 Effective range for `-q:a` is probably 0.1-10 (unverified). If ffmpeg ignores `-q:a` then get a newer build (see ticket #[ticket:1346]).
    107 
    108100==== Example using `-b:a` ====
    109101
    … …  
    113105
    114106  '''Note:''' `-cutoff 15000` was previously recommended for this encoder, but this is now automatically applied since 2012 July.
     107
     108
     109==== Example using `-q:a` ====
     110
     111{{{
     112ffmpeg -i input.wav -strict experimental -c:a aac -q:a 6 output.m4a
     113}}}
     114
     115Effective range for `-q:a` is around 0.1-10. This VBR is experimental and likely to get even worse results than the CBR. If ffmpeg ignores `-q:a` then get a newer build (see ticket #[ticket:1346]).
     116
    115117
    116118----