Lab Case 02

H.264 Variable Frame Rate Editing Risk

Synthetic H.264 MP4 with irregular frame timing to test VFR detection and verdict priority.

✓ Synthetic fixture✓ Browser-local test✓ Reproducible

Expected top-level behaviorEditing Risk

What this case is designed to prove

Verify that H.264 does not automatically mean Supported when variable frame timing can make editing less predictable.

Sample fileh264-vfr.mp4about 74 KB · synthetic test media

Download sample

Generated from FFmpeg test patterns with deliberately irregular frame selection. It contains no user footage.

SHA-25674bc5adc131605a959357bd6acfbe343b15d93920d1c81421e3b0f53bbf185d7

VerificationFixture characteristics cross-checked with FFprobe 7.1.5 on September 30, 2026.

Sample input

Known media facts

These are the characteristics the fixture was generated to expose. MediaInfo may format some labels slightly differently across versions.

ContainerMPEG-4 / MP4

Video codecAVC / H.264

ProfileHigh

Resolution320 × 180

Nominal rate30 fps

Frame-rate modeVFR

Bit depth8-bit

Chroma4:2:0

AudioAAC / 48 kHz

Expected behavior

What ClipCompat should report

The VFR Checker should return Editing Risk rather than Supported.
Premiere and Resolve can still show their H.264 support findings, but the overall verdict should be raised to Editing Risk because the VFR finding has higher severity.
The recommended action should preserve the original and suggest a separate CFR edit copy only if timing, proxy or sync problems actually appear.

Fixture context

What the fixture confirms

FFprobe 7.1.5 confirms H.264 High profile video at 320×180 where the nominal rate is 30/1 but the average rate is 660/29 (about 22.76 fps). The fixture was generated with deliberately irregular frame selection so the browser analyzer has a reproducible timing-risk input.

Safe handling

VFR is not automatically bad. The safe advice is to avoid unnecessary conversion when the source already edits correctly.

Observed analyzer evidence

From sample facts to a practical verdict

These synthetic files were analyzed on 2026-10-11 using MediaInfo WASM and the same normalization and compatibility rules used by the checker. This run used Node.js; it was not an import or playback test in Premiere or Resolve.

H.264 Variable Frame Rate Editing Risk

Detected media: MPEG-4 · AVC · High
Image and timing: 8-bit · 4:2:0 · VFR
Premiere / Windows: Editing Risk
Resolve Free / Windows: Editing Risk

Why Premiere / Windows received this result

Variable frame rate detected
Variable frame timing can make editing, proxy matching, scrubbing or sync behavior less predictable. Reported range: 15–30 fps.
Evidence: media fact
Common Premiere editing baseline
H.264/AVC in an MP4 or MOV-style container with conventional 8-bit 4:2:0 characteristics is a common Premiere source combination.
Evidence: heuristic
Premiere documents H.264/AVC hardware decoding for MP4 media
Adobe documents hardware-accelerated decoding for MP4 media using H.264/AVC. Actual acceleration still depends on supported hardware and drivers.
Evidence: official support

Next action: Keep the original. If you see timing, proxy or sync problems, create a constant-frame-rate edit copy instead of replacing the source.

Download the same sample

A readable codec is not a guarantee of editor support. Test Required records a limit of the current rules; Supported is not an editor benchmark. Download raw MediaInfo output, normalized facts, checksums and full findings (JSON). Read the methodology.

Run the test

Open a related checker.

The same sample can intentionally produce different guidance depending on the selected editor target.

ToolVFR CheckerOpen checker →ToolPremiere Pro CheckerOpen checker →ToolDaVinci Resolve CheckerOpen checker →

Related troubleshooting guides

Variable frame rate and video editing →OBS recording editing problems →

More evidence

Compare all five Lab Cases.

Use the case index to move from a common H.264 baseline to VFR, HEVC 10-bit 4:2:2, VP9 and AV1 test media.

View all Lab Cases