Videos stripped from build via gameci/unity-build — "Can't create LinuxVideoMedia, format 0 not supported"

[gheorghiuradu]

Summary

A VideoClip in Assets/Resources/Video/ plays correctly in the Unity editor, but
is silently missing from builds produced by the game-ci/unity-builder action.
No runtime errors — the video simply never plays.

Environment

• Action: game-ci/unity-builder@v5
• Unity: 6000.4.6f1
• Target platform: StandaloneWindows64, StandaloneLinux, StandaloneOSX

Reproduction

1. Place an .mp4 in Assets/Resources/Video/
2. Load and play it at runtime via Resources.Load<VideoClip>(), or via PlayOnAwake in the editor
3. Works in the editor; produces no video in the CI build

Relevant build log

Start importing Assets/Resources/Video/Tutorial.mp4 using Guid() (VideoClipImporter)
Error: Can't create LinuxVideoMedia, format 0 not supported

What I ruled out

• Disabling Transcode in the VideoClip import settings — no change
• Re-encoding the source with several different codecs — no change
• No errors at runtime, so nothing surfaced until I read the build logs

Question

Is this expected behaviour when importing video assets inside the Linux-based
builder image, or is it a missing codec dependency in the container? Either way,
it might be worth a note in the docs; the failure is silent and cost me two days.

I found a workaround and I'll post it as an answer below.

[gheorghiuradu]

Workaround: move the video to StreamingAssets

Moving the file from Assets/Resources/Video/ to Assets/StreamingAssets/
fixes it completely. No other changes needed.

Load it at runtime with a path instead of a VideoClip reference:

var path = System.IO.Path.Combine(Application.streamingAssetsPath, "Tutorial.mp4");
videoPlayer.source = VideoSource.Url;
videoPlayer.url = path;

Why this works

The error comes from Unity's asset importer, which runs on the Linux CI
machine regardless of your build target. The importer's video backend in the
container can't handle the format, so the VideoClip is not imported and
because the failure happens at import time rather than at runtime, the player
throws nothing and you get silence.

Files in StreamingAssets are copied into the build verbatim and never touch the
asset pipeline, so the importer never gets a chance to fail. Which also explains
why disabling transcoding didn't help: the file was still trying to be imported.

Trade-off: you lose the platform-specific transcoding Unity would normally do, so
ship a format that plays everywhere you target (H.264 in an MP4 container is the
safe choice).