June 18, 2019
By Jan Ozer Contributing Editor
Featured Articles

回顾:电视直播12

It’s been a while since we looked at Telestream Wirecast, now up to version 12.0, and we were intrigued by some of the key new features in the latest three updates. This includes access to live captioning and restreaming to multiple platforms in Wirecast 10, 这两项服务都有100分钟的免费试用期. 版本11提供了推力杆转换, 而版本12增加了一个新的库存媒体库, audio mixing in Rendezvous, and a QR Code Generator, 这样你就可以更容易地将浏览者引导到外部web URL. 我将按照介绍的顺序描述它们.

对于不熟悉程序的读者, Wirecast is a Windows/Mac live video production program that can input and mix multiple audio and video inputs, add transitions, titles, and other elements, and transmit the output stream to different services and/or store an archived version off to disk. With versions starting at $695, Wirecast is cheap enough to stream simple webcam and PowerPoint tutorials or instructional videos and powerful enough for sophisticated multiple-camera live productions. [Note: Telestream changed Wirecast pricing shortly after this article went to print. There are now three tiers of Wirecast: ONE costs $249, Studio costs $449, and Pro costs $699.]

Wirecast Restream

In version 10, Telestream首次推出了无线广播网络服务, a cloud-based service that includes Wirecast Live Captions and Wirecast Restream, which allows you to send a single-input stream to multiple cloud destinations. 在以前版本的Wirecast中, 您可以传输到多个服务, but you needed sufficient processing power to encode a stream for each destination and the outbound bandwidth necessary for all streams. With Restream, you transmit a single stream into the cloud and direct that to multiple destinations, 很像Switchboard Live这样的服务.

Setup is simple. You choose and configure the services as before and select the Restream and Captions checkbox (Figure 1). Once enabled, Wirecast将对单个“池”编码进行编码, currently limited to 720p, transmit that to the cloud, and then distribute the streams to the selected services from the cloud. Clicking the Configure button next to the checkbox lets you enable or disable captions for any or all streams. Note that you must enable Restream to access Live Captions since the speech-to-text operation is performed in the cloud. However, 你可以在没有字幕的情况下回放, 这一点很重要，因为这两种服务都是收费的. 下面将详细介绍此定价的工作原理.

Figure 1. 使用Restream流到多个目的地. 点击这里查看完整尺寸的图片.

我在Facebook Live和YouTube Live上测试了Restream广播. Quality on both sites was good and glass-to-glass latency was reasonable, YouTube直播约14秒，Facebook直播约27秒. 我询问了延迟，了解到这因服务而异, 尽管Restream通常会增加10-20秒的延迟.

按每分钟/每项服务收费, 所以10分钟的流媒体服务要花40分钟. 一开始你有100分钟的空闲时间. From there, Telestream offers two packages, $25/month for 500 minutes and $0.超过5美元/分钟，或75美元/月，2000分钟和0美元.0375/minute.

Restream在我的测试中运行良好，可用性也很好. It was lovely not having to learn a completely new interface to make the function work. On the other hand, for high-volume live streamers, Restream will likely prove more expensive than third-party products like Switchboard Live which don’t share the current 720p limitation.

Live Captions

Though few casual broadcasters are legally required to caption at this point, captions are obviously highly desirable when broadcasting to deaf and hard-of-hearing people, 当广播到嘈杂的环境, 或者是那些可能在关掉声音的情况下观看的观众.

虽然视频点播的字幕现在相对简单, 实时字幕一直是一项复杂的操作. Until very recently, you had to send an audio stream of your event to a human captioner who typed the captions on a stenographic keyboard, 然后在哪里被翻译成全文, formatted as captions, 并合并到直播中. Workflows like this are cumbersome and expensive and therefore used only when absolutely necessary.

在无线广播中启用实时字幕, you select the Restream and Captions checkbox in the Output Setting dialog and then Configure to enable/disable captions (Figure 1). If your presentation has multiple audio inputs, you can designate which to caption. During the event, 无线广播网络服务转录音频, 将文本作为CEA-608格式的标题插入RTMP流, 并将流发送到服务. Captions can only be displayed by services that can handle this format and Telestream has little control over how they are displayed.

在Facebook Live上，标题显示几乎是自动的，但是标题本身很难读懂. 在评论中谈到的权利 Figure 2, the normally quiet and reserved Anthony Burokas said it best: “It's not working like normal captions, 哪些显示文本，然后更改为新文本. These captions are three lines and they “change” to move a line up, but it's not a scroll. 所以，与典型的字幕相比，它需要一点时间来适应.” He was actually being kind; I found the captions nearly impossible to read; again, see for yourself. I asked about this, and Telestream said that the player controls how the captions are displayed and there was nothing they could currently do at their end.

Figure 2. Facebook Live中的字幕设置很容易，但很难阅读.

Fortunately, 不过在YouTube Live上配置字幕比较困难, 演示文稿更容易阅读了Figure 3). Specifically, 如果你在YouTube上即时直播，你就不能添加字幕, 只有当你把活动安排在以后的时候. Then you have to dig to the bottom of the Stream Settings screen to enable closed captions and set them up as Embedded 608/708. Obviously, these are YouTube issues, not Wirecast, 但如果你打算用Wirecast为YouTube直播活动配标题, 给自己足够的时间来弄清楚如何让它工作. The captions worked as advertised in our live tests, but seemed quirky in our tests thereafter. 欢迎您试用该文件, 但YouTube可能会用他们自己的后期处理字幕来代替, and in any event, 我们不确定你会从标题的角度看到什么.

Figure 3. YouTube上的字幕更容易阅读.

Telestream claims that Live Captions is more than 90% accurate with clean audio input, 我觉得这很乐观, 开始的时候两种转录方式都很糟糕.. 播放两个视频，你就会明白我的意思了. 语音转文本算法是基于机器学习的, 因此，随着时间的推移，应该通过识别名字来改善, technical words, and acronyms. 转录有五种语言版本, English (US and UK), French, Portuguese (Brazilian), and Spanish.

As with Restream, you get 100 minutes free with your new or upgraded version of Wirecast; thereafter, Telestream offers two plans. 一种是每月60美元，包括500分钟和0美元的费用.12/minute for overages. 第二个是175美元/月，包括2000分钟和0美元.0875/minute overage charge.

You pay for captioning once, even if you send the captions to multiple services. So, ten minutes of captions sent to four services costs you 10 minutes at the rate you’ve selected. Also, 因为您必须使用Restream来访问标题, 如果您只向单个服务发送标题, Restream is included; there is no separate charge. 如果您向两个或多个服务发送标题, you’ll be charged for Restream for the second and all other services.