DTV下的AD Switch和Hearing Impaired功能介绍

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前言

  本文介绍DTV下的audio language下的AD Switch和subtitle language下的Hearing Impaired功能

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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。

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总结