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VFW_E_MONO_AUDIO_HW
Meaning
Windows documents VFW_E_MONO_AUDIO_HW as “Cannot change balance because audio device is mono only”. Here, IBasicAudio balance is changed on an output path whose hardware exposes only a mono channel.
Relevant contract
Start with the filter graph, device or persisted configuration that first returned the result.
Evidence worth preserving
- Evidence 1: active audio renderer and endpoint ID.
- Evidence 2: channel count and speaker configuration.
- Evidence 3: requested balance value and device-change event.
Conditions that can produce it
- Cause 1: the selected endpoint is physically mono.
- Cause 2: a telephony or capture device reports one output channel.
- Cause 3: the renderer fell back to a mono mode after device reconfiguration.
Retry and recovery
Retry rule: Retry only after the active renderer reports at least two output channels.
Correction strategy
- Action 1: disable the balance control for mono endpoints.
- Action 2: rebuild the audio graph after selecting a stereo-capable device.
- Action 3: present volume-only controls when left-right balance has no meaning.
Example incident
A player keeps its stereo balance slider enabled after switching to a USB handset; capability-gating the control prevents it.
How it differs from nearby results
VFW_E_NO_AUDIO_HARDWARE means no usable audio device is available, whereas it means audio exists but cannot implement left-right balance.
Official Microsoft references
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