Video render fails with "Could not read from source" error

[tommy-doe]

Describe the bug

Attempting a simple video input → video output render of a source mp4 file, the jobs fails every time on the step where aerender.exe is launched, with error [STDOUT] aerender Error: After Effects error: Could not read from source. Please check the settings and try again.. All previous tasks complete successfully.

Expected Behaviour

The job completes successfully, rendering a new output video

Current Behaviour

The job fails with the following logs:
2026/02/03 15:57:28-08:00 2026/02/03 15:57:28-08:00 ==============================================2026/02/03 15:57:28-08:00 --------- Running Task2026/02/03 15:57:28-08:00 ==============================================2026/02/03 15:57:28-08:00 ----------------------------------------------2026/02/03 15:57:28-08:00 Phase: Setup2026/02/03 15:57:28-08:00 ----------------------------------------------2026/02/03 15:57:28-08:00 ----------------------------------------------2026/02/03 15:57:28-08:00 Phase: Running action2026/02/03 15:57:28-08:00 ----------------------------------------------2026/02/03 15:57:28-08:00 Running command "C:\Program Files\Python311\python.EXE" C:\Sessions\session-c4a30e960f6f4dee86e17d3409351768v4pes50z\assetroot-1f4397209bdac0f965df\.deadline\DeadlineCloudAETemp\DeadlineCloudAESubmission\scripts/call_aerender.py C:\Sessions\session-c4a30e960f6f4dee86e17d3409351768v4pes50z\assetroot-1f4397209bdac0f965df\Downloads\assetts\sea68.aep 1 C:\Sessions\session-c4a30e960f6f4dee86e17d3409351768v4pes50z\assetroot-1f4397209bdac0f965df\Downloads\assetts/sea68_SEA68.mp4 0-475 --multi-frame-rendering OFF --max-cpu-usage-percentage 90 --ignore-missing-dependencies OFF2026/02/03 15:57:28-08:00 Command started as pid: 48962026/02/03 15:57:28-08:00 Output:2026/02/03 15:57:29-08:00 Args: Namespace(project='C:\\Sessions\\session-c4a30e960f6f4dee86e17d3409351768v4pes50z\\assetroot-1f4397209bdac0f965df\\Downloads\\assetts\\sea68.aep', rqindex=1, outputpath='C:\\Sessions\\session-c4a30e960f6f4dee86e17d3409351768v4pes50z\\assetroot-1f4397209bdac0f965df\\Downloads\\assetts/sea68_SEA68.mp4', frames='0-475', chunk_size=None, index=None, multi_frame_rendering='OFF', max_cpu_usage_percentage=90, ignore_missing_dependencies='OFF')2026/02/03 15:57:29-08:00 No chunk_size and index passed in, this is not an image output.2026/02/03 15:57:29-08:00 [DEBUG] Starting aerender process with command: aerender.exe -project "C:\Sessions\session-c4a30e960f6f4dee86e17d3409351768v4pes50z\assetroot-1f4397209bdac0f965df\Downloads\assetts\sea68.aep" -rqindex 1 -s 0 -e 475 -v ERRORS_AND_PROGRESS -close DO_NOT_SAVE_CHANGES -sound OFF -mfr OFF 90 -output "C:\Sessions\session-c4a30e960f6f4dee86e17d3409351768v4pes50z\assetroot-1f4397209bdac0f965df\Downloads\assetts/sea68_SEA68.mp4"2026/02/03 15:57:37-08:00 [DEBUG] Process finished with return code: 02026/02/03 15:57:37-08:00 [STDOUT] aerender version 25.2.2x22026/02/03 15:57:37-08:00 [STDOUT] PROGRESS: Launching After Effects...2026/02/03 15:57:37-08:00 [STDOUT] rqindex 1num 12026/02/03 15:57:37-08:00 [STDOUT] aerender Error: After Effects error: Could not read from source. Please check the settings and try again.2026/02/03 15:57:37-08:00 [ERROR DETECTED] in stdout: aerender Error: After Effects error: Could not read from source. Please check the settings and try again.2026/02/03 15:57:37-08:00 [DEBUG] Errors were detected, exiting with code 12026/02/03 15:57:37-08:00 Process pid 4896 exited with code: 1 (unsigned) / 0x1 (hex)

Reproduction Steps

1. Create a new "composition from footage" and add the sea68.mp4 asset
2. Add to render queue
3. Submit job to a Windows fleet

SEA68.mp4

Environment

At minimum:

1. Operating system: macOS Tahoe 26.2
2. Version of After Effects: 25.6.0
3. Version of this package: latest as of 2026-02-03

Please share other details about your environment that you think might be relevant to reproducing the bug.

[viknith]

Thank you for cutting this issue! We will track this internally and update this issue with further information once it has been prioritized.