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-rw-r--r--libAACenc/include/aacenc_lib.h52
1 files changed, 44 insertions, 8 deletions
diff --git a/libAACenc/include/aacenc_lib.h b/libAACenc/include/aacenc_lib.h
index 6002366..fcdaca5 100644
--- a/libAACenc/include/aacenc_lib.h
+++ b/libAACenc/include/aacenc_lib.h
@@ -938,14 +938,50 @@ typedef enum
- n: Frame count period. */
AACENC_SIGNALING_MODE = 0x0302, /*!< Signaling mode of the extension AOT:
- - 0: Implicit backward compatible signaling. (default)
- - 1: Explicit SBR and implicit PS signaling.
- - 2: Explicit hierarchical signaling.
-
- The use of backward-compatible implicit signaling is recommended if the user specically
- aims at preserving compatibility with decoders only capable of decoding AAC-LC. Otherwise
- use non-backward-compatible explicit signaling.
- Bitstream formats ADTS and ADIF can only do implicit signaling. */
+ - 0: Implicit backward compatible signaling (default for non-MPEG-4 based
+ AOT's and for the transport formats ADIF and ADTS)
+ - A stream that uses implicit signaling can be decoded by every AAC decoder, even AAC-LC-only decoders
+ - An AAC-LC-only decoder will only decode the low-frequency part of the stream, resulting in a band-limited output
+ - This method works with all transport formats
+ - This method does not work with downsampled SBR
+ - 1: Explicit backward compatible signaling
+ - A stream that uses explicit backward compatible signaling can be decoded by every AAC decoder, even AAC-LC-only decoders
+ - An AAC-LC-only decoder will only decode the low-frequency part of the stream, resulting in a band-limited output
+ - A decoder not capable of decoding PS will only decode the AAC-LC+SBR part.
+ If the stream contained PS, the result will be a a decoded mono downmix
+ - This method does not work with ADIF or ADTS. For LOAS/LATM, it only works with AudioMuxVersion==1
+ - This method does work with downsampled SBR
+ - 2: Explicit hierarchical signaling (default for MPEG-4 based AOT's and for all transport formats excluding ADIF and ADTS)
+ - A stream that uses explicit hierarchical signaling can be decoded only by HE-AAC decoders
+ - An AAC-LC-only decoder will not decode a stream that uses explicit hierarchical signaling
+ - A decoder not capable of decoding PS will not decode the stream at all if it contained PS
+ - This method does not work with ADIF or ADTS. It works with LOAS/LATM and the MPEG-4 File format
+ - This method does work with downsampled SBR
+
+ For making sure that the listener always experiences the best audio quality,
+ explicit hierarchical signaling should be used.
+ This makes sure that only a full HE-AAC-capable decoder will decode those streams.
+ The audio is played at full bandwidth.
+ For best backwards compatibility, it is recommended to encode with implicit SBR signaling.
+ A decoder capable of AAC-LC only will then only decode the AAC part, which means the decoded
+ audio will sound band-limited.
+
+ For MPEG-2 transport types (ADTS,ADIF), only implicit signaling is possible.
+
+ For LOAS and LATM, explicit backwards compatible signaling only works together with AudioMuxVersion==1.
+ The reason is that, for explicit backwards compatible signaling, additional information will be appended to the ASC.
+ A decoder that is only capable of decoding AAC-LC will skip this part.
+ Nevertheless, for jumping to the end of the ASC, it needs to know the ASC length.
+ Transmitting the length of the ASC is a feature of AudioMuxVersion==1, it is not possible to transmit the
+ length of the ASC with AudioMuxVersion==0, therefore an AAC-LC-only decoder will not be able to parse a
+ LOAS/LATM stream that was being encoded with AudioMuxVersion==0.
+
+ For downsampled SBR, explicit signaling is mandatory. The reason for this is that the
+ extension sampling frequency (which is in case of SBR the sampling frequqncy of the SBR part)
+ can only be signaled in explicit mode.
+
+ For AAC-ELD, the SBR information is transmitted in the ELDSpecific Config, which is part of the
+ AudioSpecificConfig. Therefore, the settings here will have no effect on AAC-ELD.*/
AACENC_TPSUBFRAMES = 0x0303, /*!< Number of sub frames in a transport frame for LOAS/LATM or ADTS (default 1).
- ADTS: Maximum number of sub frames restricted to 4.