Stopping audio feedback when sharing a video in Zoom

Working on a trial in federal court right now, and assisting with the courtroom electronic presentation. When doing the a/v setup, I learned a valuable lesson about how to prevent feedback. I had my laptop connected to speakers and monitors with a VGA cable fed through a HDMI converter to my laptop and separate audio cable - VGA will not transmit an audio signal.

I needed to confirm that I would be able to share a PowerPoint presentation in a Zoom session with a witness testifying remotely. Initially, when I tried to play a video clip in the PowerPoint I got very loud feedback - sort of like someone banging an industrial metal drum. The IT staff for the court helped me to discover a solution to the problem.

The first step was to mute both the mic and video on Zoom.

You can still play audio through the Share Screen function even if your mic for Zoom is muted.

The next step was to adjust the audio mixer for Windows so that only the feed for the 'headphones' - the port where the audio line was connected - and the sound for PowerPoint was enabled. System sounds, sound for Zoom itself, and sounds for all other applications were all muted.

. . . scroll back and forward in the Volume mixer to find other applications you may need to mute.

Finally when sharing the PowerPoint in the Zoom session be sure to click the option to share sound and optimize video.

K-Lite Codec Pack

As previously discussed in the Tip of the Night for December 7, 2019, a video may not play in an application or on an operating system, unless the necessary codecs are installed. A codec will uncompress a video file, so it can be played. Typically video files are compressed to save storage space at the loss of some of the original resolution. These are lossy video files.

The K-Lite codec pack, available here, https://codecguide.com/, will allow Windows to play a wide range of video and audio formats. It should allow Windows Media Player to recognize most video and audio files. The Ogg video format (with an .ogg, .ogm or .ogv extension) is actually a container file which must be uncompressed before it can be played. It is not supported by Windows Media Player. See the list of supported files posted here. If you attempt to play such a file in Windows Media Player, you'll get an error like this:

If you prompt the Windows Media Player to try it, you'll get this result:

After the K-Lite Codec Pack is installed, an OGG file should play in Windows Media Player. I tested this on my PC tonight and confirmed that installing the pack made the difference.

Another common format video format which doesn't work with Windows Media Player is are Adobe Flash videos with the .flv extension.

However, if you are presenting videos with IPRO's courtroom presentation software Trial Director ,be aware that the K-Lite codec pack can cause problems. Tech support for IPRO warned me last month that the K-Lite codec pack has been known to interfere with the performance of Trial Director. It's usually recomnended that Windows Media Player be set as the default application for video and audio files when using Trial Director.

Line conditioners

Most people will have a used a power strip with a surge protector at some point - this will shut off an electrical current when the power becomes too high.

If you are setting up audio-visual equipment in a courtroom or other building with an older electrical system it may be wise to also use a line (or power) conditioner which will control the voltage which hardware receives. More modern electrical systems will have line conditioners built-in, but many older facilities will lack them.

Low voltage dips will put stress on electrical devices and cause them to fail. A line conditioner will keep the voltage with a safe range.

A typical line conditioner will look like this model:

The power cords from multiple laptops, printers, and other devices can be plugged into the line conditioner, and the line conditioner's power cord will be plugged to a wall outlet.

The line conditioner should have warning lights which indicate when the power is too high or too low.