X2

296 MPEG-4 encoder settings
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
audio can be encoded with a sample rate of 8,000, 16,000, 24,000, 32,000 or 48,000
z 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.
• For the File Header Type, choose either RAW or ADTS. The "Header" indicates an
explanatory head for the beginning of the file segment, which in fact takes up extra
space, but is required for decoding under circumstances.
- RAW indicates material which does not include a file header in audio format. The
audio material is therefore transferred directly without any special additional
information (raw).
This requires that decoding routines are able to process the material without the
explanatory file header. Especially in case "exotic" sample rates are set, this can
lead to problems during RAW encoding.
- ADTS indicates a file header type which contains information for encoded audio
material. In case of doubt, select this file header type, since fewer problems can
be expected in this case.
Object type: This provides selection between "Main" and "Low complexity".
•
Low complexity: Data is present in a form that hinders different decoding algorithms
(noise replacement), but enables others (temporal adjustment noise formation).
•
Main: This sets other focuses in the encoding, and other decoder algorithms can be
used.
material. As with video material, the audio format should be considered for playback later.
AAC
H
Note: For example, Apple iPod requires "low complexity encoding". However, you don't
need to worry if you select the right preset for Apple iPod in the export dialog.
Multiplexer
The multiplexer is a component of the encoder which combines audio and video streams.