diff options
Diffstat (limited to 'libAACenc/include')
| -rw-r--r-- | libAACenc/include/aacenc_lib.h | 52 |
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. |