A sign is not a diagnosis
A negative reported time can be alarming when a production expects its programme to begin at zero. The useful first question is which timing field is negative and how the container presents the recording. Preserve the source and inspect the actual first displayed picture and audible content.
Do not remove the value solely to make an inventory column look tidy. Another stream or caption sidecar may depend on the existing relationship. A transformation that helps a standalone derivative can harm a package intended to align with external production references.
FFmpeg documents timestamp preservation and start-shifting controls with interaction caveats. Use the installed version's behaviour for the intended output. A control name that promises preservation should not be treated as proof that later muxing leaves every timestamp unchanged.
Choose a new origin deliberately
For an owned delivery requiring a zero-based timeline, record the shift and apply a coherent policy to associated assets. Compare a recognisable event before and after processing. Keep the original timing note so the output can be related back to source material.
Imagine a caption file prepared against the source's presentation timeline. Moving only the picture's origin can leave every caption displaced even if the picture now begins at the preferred numeric value. The successful numeric change has not completed the package task.
Review the beginning, an intermediate event and the ending. If the delivered version plays correctly and matches its sidecars, label it as the zero-based derivative and retain the source. If there is an unexplained discrepancy, preserve the logs and investigate before promoting it to master.
Questions answered
Does any negative timestamp mean a file is corrupt?
No. Identify the field, container behaviour and actual presentation.
Can I shift only the picture and ignore its captions?
Only if their intended association remains correct. Verify the complete package.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.