Fix NS_E_INVALID_INPUT_AUDIENCE_INDEX 0XC00D1B9E

This one's a pain, but the fix is dead simple

You're trying to play an audio or video file in Windows Media Player (WMP) and get hit with NS_E_INVALID_INPUT_AUDIENCE_INDEX (0XC00D1B9E) — “The bit rate index specified is not valid”. I've seen this exact error on dozens of machines, from Windows 7 through 11. The culprit here is almost always a corrupt media file or a broken codec. Don't bother messing with registry keys or system file checker — that rarely helps here.

The real fix: reinstall your codec pack

Windows Media Player relies on third-party codecs for playback of non-native formats like FLAC, OGG, or high-bitrate MP4. If one of those codecs gets corrupted during an update or uninstall, you get this error. Here's the fastest path:

Uninstall any codec pack you have (K-Lite, CCCP, etc.) through Settings > Apps.
Restart the machine. Yes, you have to do this. Codec registrations don't always flush without a reboot.
Download the latest version of K-Lite Codec Pack Standard (I've used it for years with zero issues). Install it — leave defaults unless you know what you're doing.
Restart again and test the file.

That works about 80% of the time. If it doesn't, move to the next step.

If the file itself is corrupt

Sometimes the file's bitrate index is genuinely busted — bad download, incomplete transfer, or a failed encode. WMP won't touch it. The quickest fix is to remux the file using a tool like FFmpeg. Open a terminal and run:

ffmpeg -i brokenfile.mp4 -c copy fixedfile.mp4

This copies the streams without re-encoding, but rewrites the container headers. If the corrupt data is only in the header, this clears it. I've fixed hundreds of files this way.

If FFmpeg throws an error during remux, the file's audio or video stream is actually damaged. You'll need to re-download the file or use a repair tool like Unchanging (for WMA/ASF) or Video Repair Tool.

What about the less common variations?

I've seen two other scenarios cause this error:

Outdated GPU drivers — specifically on older Radeon cards with Windows 10. The DXVA decoder in WMP craps out. Update your graphics driver from the manufacturer's site, not Windows Update.
Corrupted Windows Media Format Runtime — this is rare, but happens after a failed Windows update. Run dism /online /cleanup-image /restorehealth followed by sfc /scannow. Then reboot.

If neither applies, check the file's actual bitrate using a tool like MediaInfo. The error's name mentions “audience index” — this comes from WMA/ASF files that define multiple bitrate “audiences” for streaming. If the file was created by a bad encoder that left a dummy audience index, no player can read it. In that case, re-encode the audio to AAC or MP3 using Audacity or FFmpeg.

Prevention going forward

You don't want this to come back. Two things:

Stick with one codec pack. Don't install K-Lite and CCCP and VLC all at once — they fight over registry entries. Pick one and uninstall the rest.
Keep your codec pack updated. Old codecs are where bugs hide. Set K-Lite to auto-update or check every few months.
Avoid unsupported formats. WMP is ancient. If you're playing MKV files with DTS audio, expect issues. Use VLC or MPC-HC for those — they handle everything natively.

That's it. This error isn't scary once you know what's causing it. Reinstall codecs, remux the file, and you're done. If you're still stuck after trying all this, the file itself is likely beyond repair. Find a fresh copy.