X3

MPEG-4 encoder settings
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AMR
AMR involves a parametric codec with different data rates between 4.75
and 12.2 kbit/s. The 12.2-kbit/s settings throughly corresponds with the
GSM-EFR codec in terms of algorithm and audio quality.
This audio format is used by mobile telephones for transferring the
conversation and is optimized for encoding conversation (voices). Low bit
rates provide compensation for mobile phones in case of transfer errors, i.e.
bad reception. Depending on the signal strength, the compression increases
or decreases to enable the best possible quality for a conversation. The
AMR sound, on the other hand, encodes a fixed sample rate of 8,000 Hz
compared to AAC sound.
The advanced AMR audio menu includes the following settings options:
The bit rate can be set between 4.75 and 12.2kbit/s. The higher the bit rate,
the greater the file size and the higher level of audio quality. The standard
settings provide a bit rate of 7.4 kbit/s. The highest bit rate for this format is
more suited for transferring conversations.
AAC
The AAC audio was developed by MPEG, the Moving Picture Experts Group
(Dolby, Fraunhofer Institut für Integrierte Schaltungen in Erlangen, AT&T,
Nokia, Sony) as an audio data compression process, that was specified as
a further development of MPEG-2 Multichannel in the MPEG-2 standard.
It's also a further development of MPEG-2 audio. This format is equally
suitable for encoding general audio information and not especially optimized
for certain types of audio material. As with video material, the audio format
should be considered for playback later.
AAC audio can be encoded with a sample rate of 8,000, 16,000, 24,000,
32,000 or 48,000 Hz and in mono and stereo sound, respectively. By
default, the sound is set to 48,000 Hz stereo. The higher the sample rate is,
the larger the resulting file and higher the audio quality.
The advanced AAC audio menu includes the following settings options:
 The bit rate can be set between 6 and 512 kbit/s. 160 kbits/s is active by
default. The higher the value is, the larger the resulting file and higher the
audio quality. After a certain limit, additional improvements to audio quality
will not be perceived. Bit rates under 64 kb/s are not recommended.
 As an MPEG version, set MPEG-4 or the older, proven MPEG-2 format.