• Rostislav Pehlivanov's avatar
    aaccoder: add a new perceptual noise substitution implementation · 38fd4c2e
    Rostislav Pehlivanov authored
    This commit finalizes the PNS implementation previously added to the encoder
    by moving it to a seperate function search_for_pns() and thus making it
    coder-generic. This new implementation makes use of the spread field of
    the psy bands and the lambda quality feedback paremeter. The spread of the
    spectrum in a band prevents PNS from being used excessively and thus preserve
    more phase information in high frequencies.  The lambda parameter allows
    the number of PNS-marked bands to vary based on the lambda parameter and the
    amount of bits available, making better choices on which bands are to be marked
    as noise. Comparisons with the previous PNS implementation can be found
    here: https://trac.ffmpeg.org/attachment/wiki/Encode/AAC/
    
    This is V2 of the patch, the changes from the previous version being that this
    version uses the new band->spread metric from aacpsy and normalizes the
    energy using the group size. These changes were suggested by Claudio Freire
    on the mailing list. Another change is the use of lambda to alter the
    frequency threshold. This change makes the actual threshold frequencies
    vary between +-2Khz of what's specified, depending on frame encoding performance.
    Reviewed-by: 's avatarClaudio Freire <klaussfreire@gmail.com>
    Signed-off-by: 's avatarMichael Niedermayer <michaelni@gmx.at>
    38fd4c2e
aaccoder.c 50.2 KB