bytedeco/javacv

FFmpegFrameGrabber should throw an exception when attempting to access stream metadata before calling start()

Open

#2382 opened on Feb 19, 2026

View on GitHub
 (4 comments) (0 reactions) (0 assignees)Java (6,985 stars) (1,583 forks)batch import
enhancementhelp wantedquestion

Description

As stated in the title, when using FFmpegFrameGrabber, if start() is not called beforehand, methods such as getImageWidth() will return 0. This behavior may cause errors to propagate downstream and lead to issues that are more difficult to trace. I believe an IllegalStateException should be thrown immediately to clearly indicate that this operation is invalid.

Contributor guide

Tech stack
java
Domain
backendapi
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic understanding of FFmpegFrameGrabber lifecycle
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
90
Research direction
Look at the source code of FFmpegFrameGrabber (likely in a file like FFmpegFrameGrabber.java) to identify methods such as getImageWidth(), getImageHeight(), etc. that return metadata. Currently they return 0 when start() has not been called. The fix is to check if start() has been called (possibly using a flag) and throw an IllegalStateException with a descriptive message. Ensure consistent behavior across all such metadata access methods. No linked PRs or assignees exist, so this is available for implementation.