User manual

148 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: