Audio decoder, apparatus for generating encoded audio output data and methods permitting initializing a decoder

An apparatus for generating a bit stream of encoded audio data representing a sequence of audio sample values of an audio signal, wherein the bit stream of encoded audio data comprises a plurality of frames, wherein each frame includes associated encoded audio sample values, wherein the apparatus comprises:

• a special frame provider configured to provide at least one of the frames as a special frame, the special frame comprising encoded audio sample values associated with the current frame and additional information, wherein the additional information comprises encoded audio sample values of a number of frames preceding the special frame, wherein the encoded audio sample values of the preceding frames are encoded using the same codec configuration as the special frame, and wherein the number of preceding frames is sufficient to initialize a decoder to be in a position to decode the audio sample values associated with the current frame if the special frame is the first frame upon start-up of the decoder;
• and
• an output configured to output the bit stream of encoded audio data,
• wherein the following applies:
• the first element of every frame is an extension element of type ID_EXT_ELE_AUDIOPREROLL,
• the corresponding extension element shall be set-up as described in the following Table 2:
• TABLE 2
• Setup of the extension element for AudioPreRoll( )
• usacExtElementType
• ID_EXT_ELE_AUDIOPREROLL
• usacExtElementConfigLength
• 0
• usacExtElementDefaultLengthPresent
• 0
• usacExtElementPayloadFrag
• 0
• if pre roll data is present, this frame shall start with the following bit sequence:
• “1”:
• usacIndependencyFlag,
• “1”:
• usacExtElementPresent (referring to audio pre roll extension element),
• “0”:
• usacExtElementUseDefaultLength (referring to audio pre roll extension element),
• if no pre roll data is transmitted, the extension payload shall not be present (usacExtElementPresent=0),
• the pre roll frames with index “0” shall be independently decodable, i.e. usacIndependencyFlag shall be set to “1”.

A method for decoding a bit stream of encoded audio data, wherein the bit stream of encoded audio data represents a sequence of audio sample values and comprises a plurality of frames, wherein each frame includes associated encoded audio sample values, comprising:

• determining whether a frame of the bitstream of encoded audio data is a special frame comprising encoded audio sample values associated with a current frame and additional information, wherein the additional information comprise encoded audio sample values of a number of frames preceding the special frame, wherein the encoded audio sample values of the preceding frames are encoded using the same codec configuration as the special frame, wherein the number of preceding frames is sufficient to initialize a decoder to be in a position to decode the audio sample values associated with the current frame if the special frame is the first frame upon start-up of the decoder;
• and
• initializing the decoder if it is determined that the frame is a special frame, wherein the initializing comprises decoding the encoded audio sample values included in the additional information before decoding the encoded audio sample values associated with the current frame,
• wherein the following applies:
• the first element of every frame is an extension element of type ID_EXT_ELE_AUDIOPREROLL,
• the corresponding extension element shall be set-up as described in the following Table 2:
• TABLE 2
• Setup of the extension element for AudioPreRoll( )
• usacExtElementType
• ID_EXT_ELE_AUDIOPREROLL
• usacExtElementConfigLength
• 0
• usacExtElementDefaultLengthPresent
• 0
• usacExtElementPayloadFrag
• 0
• if pre roll data is present, this frame shall start with the following bit sequence:
• “1”:
• usacIndependencyFlag,
• “1”:
• usacExtElementPresent (referring to audio pre roll extension element),
• “0”:
• usacExtElementUseDefaultLength (referring to audio pre roll extension element),
• if no pre roll data is transmitted, the extension payload shall not be present (usacExtElementPresent=0).
• the pre roll frames with index “0” shall be independently decodable, i.e. usacIndependencyFlag shall be set to “1”.