The `GlUtil` wrappers for attributes/uniforms allocate buffers that are passed into OpenGL, and it seems that the distorted output was caused by these buffers being garbage collected.
The issue was difficult to reproduce manually. Add a test that does repeated transcodes in a loop (marked `@Ignore` for now because it runs for a long time and requires network access so may be flaky) to make it easier to run many transcodes and look for inconsistent output. For now the consistency check is just based on the file size which is very likely to change if the actual video frames change.
Verified that the test fails before, and passes once the attributes and uniforms are stored in fields as in this CL.
PiperOrigin-RevId: 410581706
e1e54b3e15