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Produce a Professional-Quality Webcast

It's all about finding the right technologies and creating the best workflow, especially when streaming live video.

Computer playback audio is increasingly a consideration for webcasts, and this requires audio adapter cables, often paired with a DI (or Direct Box) in order to minimize ground loops. Webcasts often begin with a static slide and background music, so this audio input is a consideration. Because the slide and music broadcast usually goes through the same soundboard as the microphone inputs, this means audio level balancing needs to be done before the holding slide goes live. Music and additional holding slides are typically played during breaks and at the end of a webcast. Holding slides can be played back from a connected laptop or via the video switcher if it has a supported media player.

Technical Direction, Tally Lights, and Talkback

The technical director who operates the video switcher needs to be in contact with the audio technician and camera operators and, typically, does so using an intercom talkback system. Tally lights can also be used to give the camera operators and talent a visual indication of which video camera is live and which are on standby.

Intercom-only systems usually use standard three-pin XLR audio cables and intercom with integrated tally light signals can use special four-pin XLR cables. Newer intercom and tally light systems replace XLR cable with optical fiber cable that can also transmit two-way HDMI or HD-SDI video signals.

The technical director can view each of the video inputs and communicate with the camera operators regarding their next shot, any technical adjustments, when they are on standby, and when they are live. The live video signal is called the program feed, and the video signal that is on standby is called the preview. Traditionally, the technical director can see each camera input on a separate monitor, but this requires numerous monitors and a large control room. Many video switchers have a multiview output that allows the technical director to see each of the inputs and the preview and program feeds on a single HD monitor.

Capture Cards

The audio from the soundboard is sometimes connected to the video switcher if it can handle audio, but otherwise it connects directly with the webcast encoder, a computer with compliant audio and video inputs. Some capture cards require embedded HDMI or HD-SDI audio, while others allow for analog XLR audio inputs.

The capture card can be used to scale the video signal, but this can also be done with the encoding software and the graphics card or encoding hardware if the webcast is being broadcast at a lower resolution than the input. If encoding hardware is being used, it can often connect directly with the streaming server. Otherwise, a software interface is used.

Choosing Codecs and Settings for the Live Stream

Webcast interfaces allow controls for the video resolution, codec, bitrate, and frame rate and recording of the live stream. The H.264 codec is a modern codec that balances high-quality and low-quality bitrates, but webcasters should note that the resulting encode, an .F4V file, cannot be edited with traditional editing software. An alternate recording should be made for the webcast archive.

Simply re-uploading the archive recording usually results in a less-than-ideal viewing experience for on-demand viewers unless the holding slide and music before the webcast, during any breaks, and after the webcast can be edited out.

A pass-through or auxiliary output is often taken from the video mixer or the capture card, and this signal can be recorded to an external HDMI or HD-SDI video recorder. Some video switchers with software control panels allow software-controlled archive recording using secondary video capture cards in the encoder or when paired with compatible external encoders.

Whether the technical director is switching on a software or hardware control panel, he needs to consider that the webcasting codec is a Long Group of Pictures (LongGOP) codec, which means that there is one reference I-frame every 15 frames (one-half second) and the 14 frames that follow this I-frame reference change from the original I-frame. Webcasters typically push the codec's bitrate-to-frame size ratio. This does not leave any overhead if there is too much motion or change of both the foreground and background. Outdoor scenes involving water are where many on-camera codecs fail, but for the webcaster, a codec fail can occur if the technical director uses a simple cross-dissolve. The reason: Every single pixel across the entire raster is completely different from one frame to the next for the duration of the cross-dissolve. This is where LongGOP codecs fail.

Fortunately, the recovery happens quickly, but if a cross-dissolve causes a codec fail, then the webcaster needs to increase the bitrate, reduce the video resolution, or not use cross-dissolves. Avoiding cross-dissolves is probably the single biggest difference between live-switching for a webcast and live-switching for all other mediums.

Webcasters can set up their own streaming servers, but streaming services offer pay-per-use and monthly webcasting packages that offer scalability and additional features such as adaptive bitrate support, social media sharing, support on mobile devices, embed codes for ease of website integration, and embed domain restrictions to protect webcasts from being shared on other domains.

When determining the webcast bitrate, the webcaster needs to consider the availability of adaptive bitrate encoding which would allow for lower bitrate versions or if a single bitrate is being used. If the bitrate is too high, the video playback may stall and buffer if individual users cannot sustain the download speed required. On the webcaster's end, the upload speed is more important than the download speed, so it's best to test the internet connection's upload speed. On cable and DSL internet connections, this is typically lower than the download speed. Fiber internet connections usually have the same upload and download speeds.

Ultimately the most important technical factors in producing a successful webcast are careful consideration of the entire wiring diagram and that each piece of equipment can connect with the next one down the line.

This article appears in the forthcoming 2013 Streaming Media Industry Sourcebook.

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