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Preface
本文介绍DTV下的audio language下的AD Switch和subtitle language下的Hearing Impaired功能
1. audio language之AD Switch
1.1 Introduction
Auxiliary audio function, the options are On/Off, generally used in the case of visual impairment, some areas require the name abbreviation VI
1.2. Category
There are two types of AD, namely Receiver-Mixed AD and Broadcast-Mixed AD.
1.2.1. Receiver-Mixed AD
This method is the most commonly used AD type in Europe. Its audio track does not need to transmit complete audio, but only needs to transmit the sound of amblyopia, and then mix it with the main audio track for output;
1.2.2. Broadcast-Mixed AD
This method is more common in Egypt, Thailand, etc. Its audio track transmits complete audio, which is equivalent to an independent audio track. It does not need to be mixed with the main audio track, but can be directly cut to the audio track. ,The ISO639 language codes of Broadcast-Mixed audio tracks are "qad" and "nar";
1.3 Identification method
| audio_type | description | Chinese description |
|---|---|---|
| 0x00 | Undefined | main track |
| 0x01 | Clean effects | Removed some ambient sounds and only kept the human voice |
| 0x02 | Hearing impaired | hearing impairment |
| 0x03 | Visual impaired commentary | visual impairment |
| 0x03~0x0F | Reserved | reserved |
| mix_type | Auxiliary stream type | describe | Features |
|---|---|---|---|
| 0 | Reciever-MIX | The auxiliary audio track is transmitted separately from the main audio track and synthesized locally at the receiving end. | To set the volume of AD audio track stream separately, it will not affect the volume of Nomal audio track stream. |
| 1 | Broadcast-MIX | The auxiliary track is transmitted together with the main track and synthesized in advance at the send end. | Customers decode according to the normal main audio track to avoid some receiving machines not supporting it. |
| editorial_classification | describe |
|---|---|
| 0x00 | Main audio,the classification shall not be used for broadcast-mix audio |
| 0x01 | Audio description for the visually impaired |
| 0x02 | Clean audio for the hearing impaired |
| 0x03 | Spoken subtitle for the visuall impaired |
| 0x04 | Dependent paremetric data stream |
| 0x05~0x16 | Reserved for future use |
| 0x17 | Unspecific supplementtary audio for the general audience |
| 0x18~0x1F | User defined |
| Audio purpose | audio_type | mix_type | editorial_classification |
|---|---|---|---|
| Main audio (see note 3) | 0x00 or 0x01 | 1 | 0x00 |
| Audio description (broadcast mixed) | 0x00, 0x01 or 0x03 | 1 | 0x01 |
| Audio description (receiver mixed) | 0x03 | 0 | 0x01 |
| Clean audio | 0x02 | 1 | 0x02 |
| Parametric data dependent stream | 0x02 | 0 | 0x04 |
| Spoken subtitles (broadcast-mix) | 0x00, 0x01 or 0x03 | 1 | 0x03 |
| Spoken subtitles (receiver-mix) | 0x03 | 0 | 0x03 |
| Unspecific audio for the general audience | any | 0 or 1 | 0x17 |
| user defined | any | 0 or 1 | 0x18~0x1F |
NOTE 1: audio_type is broadcast in the ISO_639_language descriptor.
NOTE 2: mix_type and editorial_classification are broadcast in the supplementary_audio descriptor.
NOTE 3: The supplementary_audio descriptor is optional in this case.
As shown in the table above, when audio_type is 0x00, 0x01 or 0x03, mix_type is 1, and editorial_classification is 1, it is Broadcast-mixed AD; when audio_type is 0x03, mix_type is 0, and editorial_classification is 1, it is Receiver mixed AD. If the above valid information is not parsed, check whether the language code in ISO_639_Language_code is "NAR" or "QAD". If so, it will be judged as Broadcast-mixed AD.
For support of Spoken subtitles, [Mandatory] requires Broadcast-mixed AD and Receiver mixed AD that are equivalent to Audio description for VI icon display and audio track processing.
1.4 Code stream analysis
1.5 audio priority
When the AD Switch is ON, the AD track has the highest priority. That is, after changing the audio language track, switching from other programs to this program or turning off and on again under this program, AD will still have priority. If AD Switch is off, the AD track has the lowest priority.
2. subtitle language之Hearing Impaired
2.1. Introduction
Auxiliary subtitle function, the options are On/Off, generally used in the case of hearing impairment, the subtitles present the audio content for easy understanding, the name is abbreviated HOH
2.2. Identification method
| subtitling_type | describe |
|---|---|
| 0x00 | reserved for future use |
| 0x01 | EBU Teletext subtitles |
| 0x02 | associated EBU Teletext |
| 0x03 | VBI data |
| 0x04~0x0F | revered for future use |
| 0x10 | DVB subtitles (normal ) with no monitor aspect ratio criticality |
| 0x11 | DVB subtitles (normal ) for display on 4:3 aspect ratio monitor |
| 0x12 | DVB subtitles (normal ) for display on 16:9 aspect ratio monitor |
| 0x13 | DVB subtitles (normal ) for display on 2.21:1 aspect ratio monitor |
| 0x14 | DVB subtitles (normal ) for display on a high definition monitor |
| 0x15 | DVB subtitles(normal ) with plano-stereoscopic disparity for display on a high definition monitor |
| 0x16~0x1F | reverved for future use |
| 0x20 | DVB subtitles (for the hard of hearing ) with no monitor aspect ratio |
| 0x21 | DVB subtitles (for the hard of hearing) for display on 4:3 aspect ratio monitor |
| 0x22 | DVB subtitles (for the hard of hearing) for display on 16:9 aspect ratio monitor |
| 0x23 | DVB subtitles (for the hard of hearing) for display on 2.21:1 aspect ratio monitor |
| 0x24 | DVB subtitles (for the hard of hearing) for display on a high definition monitor |
如上表，当subtitling_type为0x20~0x24时，代表存在H.O.H字幕
2.3. Code stream analysis
2.4. subtitle priority
In the case of Hearing Impaired ON, HOH subtitles have the highest priority. That is, after changing the subtitle language subtitles, switching to this program from other programs or shutting down and restarting under this program, HOH subtitles will still have priority. If Hearing Impaired is OFF, HOH subtitles have the lowest priority.