What is Variable Frame Rate?
Variable frame rate video allows frame durations, and therefore the number of frames displayed per second, to change over time. Presentation timestamps specify when each frame should appear.
How Variable Frame Rate works
VFR media schedules pictures through individual presentation timestamps instead of assuming equal spacing throughout the stream. A quiet screen recording may hold one image longer, while a busy interval presents new images more frequently. Containers and processing tools must preserve the timing time base as well as frame order. It appears often at ingest and may be retained or converted to a fixed cadence before editing, analysis, packaging, or device delivery.
Key facts
- An average frame-rate field cannot reconstruct VFR timing; two files with the same frame count, duration, and average may have very different per-frame presentation intervals.
- Converting VFR to a constant cadence requires dropping, duplicating, blending, or interpolating pictures, each of which changes motion portrayal and can affect frame-addressed annotations.
- Audio synchronization follows timestamps rather than frame ordinal numbers, so assigning evenly spaced times to VFR pictures can create progressive drift even when every frame is retained.
When Variable Frame Rate matters
Preserve timestamps when processing phone or screen recordings so audio synchronization and motion timing remain correct. Software that assumes a constant rate may seek inaccurately, duplicate frames, or drift out of sync.