BK-21A Overview and Use Cases

What Is the BK-21A?

The OREI BK-21A is an 8K 2 inputs, 1 output HDMI switch with audio extraction. It allows you to connect two HDMI source devices to one TV, monitor, or projector while also extracting audio through Optical or 3.5mm stereo output.

It is useful when your display has limited HDMI inputs, but you want to connect two devices such as a PlayStation, Xbox, Blu-ray player, PC, streaming device, Roku, Fire TV, cable box, or media player.

The BK-21A supports HDMI 2.1, HDCP 2.3, with a video bandwidth of 48Gbps. It supports video resolutions up to 8K@60Hz, 4K@120Hz, and 1080p@240Hz. It also supports HDR10+, Dolby Vision, VRR, ALLM, and FVA.

Unlike the BK-21, the BK-21A also includes Optical and 3.5mm audio outputs, making it useful when you want to send video to your TV while also sending audio to a soundbar, amplifier, speakers, or headphones.

IMPORTANT — BK-21A Is NOT a Seamless HDMI Switch

The BK-21A is not a seamless switch.

This means that when you switch from one HDMI input to the other, the display will usually show a black screen for a moment while the HDMI signal reconnects.

This is normal. The TV or monitor needs time to detect the new HDMI signal, complete the HDMI handshake, and display the image again.

In most setups, the black screen may last a second or two. In some cases, it may take longer depending on:

• The TV or monitor being used 
• The resolution and refresh rate 
• The HDMI cable quality 
• The source device 
• Whether 8K@60Hz, 4K@120Hz, HDR, VRR, or Dolby Vision is being used 

The BK-21A switches between HDMI sources, but it does not provide instant or zero-delay switching.

IMPORTANT — Auto Switching Depends on HDMI 5V Signal Detection

The BK-21A supports auto switching, but it works by detecting the 5V signal coming from the connected HDMI source device.

In simple terms, the switch looks for which HDMI source appears to be “active.”

If one source is connected and then another source is plugged in or powered on, the BK-21A can automatically switch to the newly detected source.

However, many modern streaming devices do not fully turn off. Devices such as Apple TV, Fire TV Stick, Google Chromecast, Roku, and similar media players often go into standby mode instead of shutting down completely. Even in standby, they may continue sending a 5V signal through HDMI.

Because of this, the BK-21A may still detect that device as active, even when the customer thinks it is “off.”

For example:

If you have an Apple TV connected to Input 1 and a PlayStation 5 connected to Input 2, the BK-21A may switch to Apple TV when the PS5 is turned off because the Apple TV is still sending an HDMI 5V signal.

But when you later turn the PS5 back on, the switch may not automatically switch away from Apple TV because the Apple TV never fully stopped sending its HDMI 5V signal.

In this type of setup, manual switching using the front panel button or included remote may be needed.

IMPORTANT — Audio Extraction Depends on the Audio Format

The BK-21A can extract audio through Optical and 3.5mm output, but the audio format must match the capabilities of the output being used.

The HDMI output can pass high-quality HDMI audio formats such as LPCM, Dolby Digital, Dolby TrueHD, Dolby Atmos, DTS, DTS-HD Master Audio, and related formats.

The Optical output supports LPCM, Dolby, and DTS up to 5.1CH.

The 3.5mm analog output supports LPCM 2CH stereo only.

If you are using the 3.5mm output, set your source device to PCM, LPCM, or Stereo. If the source is sending Dolby, DTS, Bitstream, or surround audio, the 3.5mm output will not work because it only supports stereo analog audio.

Ports and Panel Layout

Step-by-Step Setup

1. Connect your first HDMI source device to HDMI IN 1 on the BK-21A. 
2. Connect your second HDMI source device to HDMI IN 2. 
3. Connect the HDMI OUT port to your TV, monitor, or projector. 
4. Connect your audio device if needed: 
   • Use Optical for a soundbar, AVR, or amplifier. 
   • Use 3.5mm L/R for stereo speakers, headphones, etc. 
5. Connect the included 5V power adapter to the BK-21A. 
6. Turn on your TV/display, source devices, and audio device. 
7. Use the front-panel SWITCH button or included IR remote to select Input 1 or Input 2. 
8. If using auto switching, long press the SWITCH button for 3 seconds to enable or disable auto switching. 
9. If audio extraction does not work, check the source audio format and set it to a format supported by the output you are using. 

HDMI Cable Requirement — Critical

For 8K@60Hz and 4K@120Hz, use high-quality Ultra High-Speed Certified HDMI 2.1 cables under 15 feet.

Understanding the EDID DIP Switch

The BK-21A includes an EDID DIP switch that helps control what video and audio capability the source device detects.

Use a 2CH PCM EDID setting when using the 3.5mm analog output.

Use a 5.1CH EDID setting when using Optical with a soundbar or AVR that supports Dolby/DTS 5.1.

Use the default copy EDID setting when you want the source device to follow the connected display’s reported capabilities.

What Source Devices Is the BK-21A Compatible With?

The OREI BK-21A is compatible with HDMI source devices such as:

• PlayStation 5 
• Xbox Series X/S 
• Apple TV 
• Fire TV Stick 
• Roku 
• Google Chromecast 
• Blu-ray players 
• Cable boxes 
• Satellite boxes 
• Gaming PCs 
• Laptops with HDMI output 
• Media players 

For 8K@60Hz or 4K@120Hz, the source device, display, HDMI cables, and EDID settings must all support the required HDMI 2.1 bandwidth.

What Audio Devices Is the BK-21A Compatible With?

The BK-21A is compatible with audio devices that accept Optical or 3.5mm stereo input.

It can be used with:

• Optical soundbars 
• AVRs with Optical input 
• Optical amplifiers 
• Powered speakers 
• Stereo amplifiers 
• Headphones 
• 3.5mm speaker systems 

For Optical audio, the connected device must support the audio format being sent, such as LPCM, Dolby, or DTS 5.1.

For 3.5mm audio, the source must be set to PCM, LPCM, or Stereo.

What Displays Is the BK-21A Compatible With?

The BK-21A is compatible with HDMI displays such as:

• TVs 
• Monitors 
• Projectors 
• Gaming displays 
• 8K displays 
• 4K@120Hz displays 

The final resolution and refresh rate will depend on the source device, display, HDMI cables, and EDID settings.

Frequently Asked Questions

Q: What is the OREI BK-21A used for? 
A: The BK-21A is used to connect two HDMI source devices to one TV, monitor, or projector while also extracting audio through Optical or 3.5mm output.

Q: How is BK-21A different from BK-21? 
A: The BK-21A includes Optical and 3.5mm audio extraction, while the BK-21 is mainly a 2x1 HDMI switch without separate audio outputs.

Q: Is the BK-21A a seamless switch? 
A: No. The BK-21A is not a seamless switch. When switching inputs, the display will usually go black for a second or two while the HDMI signal reconnects.

Q: Why do I see a black screen when switching inputs? 
A: This is normal. The display needs time to detect the new HDMI signal and complete the HDMI handshake. The delay can vary depending on the display, source device, resolution, refresh rate, and HDMI cables.

Q: Does auto switching work with Apple TV, Fire TV Stick, Chromecast, or Roku? 
A: Auto switching may not work consistently with these devices because they often stay in standby mode and continue sending a 5V HDMI signal. The BK-21A may still detect them as active even when they appear to be off.

Q: Why does the switch stay on Apple TV even when I turn on my PS5? 
A: Apple TV may still be sending a 5V HDMI signal while in standby. Since the BK-21A still sees Apple TV as active, it may not automatically switch to the PS5. Use the front button or remote to switch manually. This applies to other devices such as Fire TV Stick, Roku Stick, Chromecast, etc. as well.

Q: How do I turn auto switching on or off? 
A: Yes. Long press the SWITCH button for 3 seconds to enable or disable auto switching.

Q: Can I display both HDMI sources at the same time? 
A: No. The BK-21A can display only one HDMI source at a time.

Q: Can I use a capture card to record games from my PlayStation or Xbox? 
A: This device is HDCP compliant and will not bypass HDCP-protected content for capture cards.