文章目录
前言
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 简介
辅助音频功能，选项有On/Off，一般用于有视力障碍的情况下，部分地区要求使用名称缩写V.I.
1.2. 类别
AD的类型有两种，分别是Receiver-Mixed AD和Broadcast-Mixed AD
1.2.1. Receiver-Mixed AD
这种方式是欧洲最常用到的AD类型，它的音轨不需要传输完整的音频，只需要传输弱视的声音即可，然后跟主音轨混音在一起进行输出；
1.2.2. Broadcast-Mixed AD
这种方式在埃及、泰国等比较常见，它的音轨是传输完整的音频，相当于一个独立的音轨，不需要跟主音轨进行混音，而是直接切到该音轨上即可,Broadcast-Mixed的音轨的ISO639语言代码是"qad"和"nar"；
1.3 识别方式
| audio_type | description | 中文描述 |
|---|---|---|
| 0x00 | Undefined | 主音轨 |
| 0x01 | Clean effects | 把一些环境声音去掉了，只保留人声 |
| 0x02 | Hearing impaired | 听力障碍 |
| 0x03 | Visual impaired commentary | 视力障碍 |
| 0x03~0x0F | Reserved | 预留 |
| mix_type | 辅助流类型 | 描述 | 特点 |
|---|---|---|---|
| 0 | Reciever-MIX | 辅助音轨与主音轨分开传输，在接收端本地合成 | 以单独设置AD音轨流的音量，不会影响Nomal音轨流的音量 |
| 1 | Broadcast-MIX | 辅助音轨与主音轨一起传输，在发送端提前合成 | 客户按正常的主音轨解码，避免部分接收机器不支持 |
| editorial_classification | 描述 |
|---|---|
| 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.
如上表，当audio_type 为 0x00, 0x01 or 0x03，mix_type 为 1，editorial_classification 为1 时，为Broadcast-mixed AD；当audio_type 为 0x03，mix_type 为 0，editorial_classification 为1 时，为Receiver mixed AD。如未解析到上述有效信息，则检查ISO_639_Language_code中的语言码是否为“NAR”或“QAD”，如果有则判为Broadcast-mixed AD。
针对Spoken subtitles的支持，【强制】要求等同于Audio description的Broadcast-mixed AD和Receiver mixed AD进行V.I.图标的显示和音轨处理。
1.4 码流分析
1.5 audio优先级
在AD Switch ON的情况下，AD音轨优先级最高，即，改变了audio language音轨后，从其他节目转到该节目或者在该节目下关机再开机，仍然是AD优先。若AD Switch为关，则AD音轨优先级最低。
2. subtitle language之Hearing Impaired
2.1. 简介
辅助字幕功能，选项有On/Off，一般用于有听力障碍的情况下，字幕将音频的内容呈现出来便于理解,名称缩写H.O.H
2.2. 识别方式
| subtitling_type | 描述 |
|---|---|
| 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. 码流分析
2.4. subtitle优先级
在Hearing Impaired ON的情况下，H.O.H字幕优先级最高，即，改变了subtitle language字幕后，从其他节目转到该节目或者在该节目下关机再开机，仍然是H.O.H字幕优先。若Hearing Impaired为OFF，则H.O.H字幕优先级最低。