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Use FFprobe for a quick screen, then inspect frame or packet timestamps if the result is unclear or the decision matters. A difference between FFprobe’s r_frame_rate and avg_frame_rate is a reason to investigate—not definitive proof. To confirm variable frame rate (VFR), check whether frame durations or presentation intervals vary.
What VFR and CFR mean
With constant frame rate (CFR), frames have consistent timing. With variable frame rate (VFR), frame durations vary. A file’s displayed or nominal frame-rate label alone does not establish its timing throughout the video or guarantee how a particular streaming platform will handle it.
Run a quick FFprobe check
Install FFmpeg, which includes FFprobe, and open a terminal in the directory containing your file. Run:
ffprobe -v error -select_streams v:0 -show_entries stream=r_frame_rate,avg_frame_rate -of default=noprint_wrappers=1 input.mp4Replace input.mp4 with your file’s path. For example, on a system where the path contains spaces, put it in quotes: "/path/to/my video.mp4". The command selects the first video stream and prints two stream-level fields. FFprobe gathers information from multimedia streams and prints it in human- and machine-readable formats; see the FFprobe documentation.
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Interpret the two fields cautiously
Compare r_frame_rate and avg_frame_rate. If they differ, treat that as a warning to inspect further. If they match, do not treat that alone as proof of CFR. This comparison is a useful screening heuristic, not a universal classification rule for every format and file.
Confirm by inspecting timing
If the field comparison is ambiguous—or you need a more dependable answer—inspect frame or packet information across the file. FFprobe can show both. The question is whether frame presentation timestamps or intervals between frames vary, rather than what single nominal rate is printed.
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To display per-frame information, you can use:
ffprobe -v error -select_streams v:0 -show_frames -of csv input.mp4For packet information, use:
ffprobe -v error -select_streams v:0 -show_packets -of csv input.mp4These commands can produce substantial output on long videos. Inspect timestamps and timing intervals throughout the file, not just at the beginning. If you need to evaluate a specific section, FFprobe also supports read intervals; consult its documentation for the relevant options and output fields. Varying frame durations or presentation intervals indicate variable timing.
Check for a QuickTime-specific VFR marker
For applicable QuickTime files, Apple documents a VFR indication field: 0 means constant frame rate, while 1 means frame durations vary. This is a format-specific marker; do not assume it exists, applies, or can classify files in every container. See Apple’s QuickTime File Format documentation.
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Choose the inspection method that fits the question
| Method | What it tells you | When to use it | Limit |
|---|---|---|---|
Compare r_frame_rate and avg_frame_rate |
Compares two stream-level rate fields | Quick initial screen | A mismatch is a warning, not proof; equality is not a universal guarantee of CFR. |
| Inspect frame or packet timing | Shows timing information across frames or packets | When the quick screen is unclear or the answer matters | Requires interpreting timestamps and intervals; output can be large. |
| Read the QuickTime VFR indication | For applicable QuickTime files, the documented value distinguishes constant timing (0) from varying frame durations (1) | When the file and metadata support this marker | Does not generalize to every container. |
Will VFR cause problems when streaming?
There is no universal acceptance rule established here: whether a file is accepted depends on the destination platform and its current ingest specifications. Check those requirements for the platform you plan to use. Do not infer that VFR alone will cause rejection—or that a CFR label guarantees acceptance.
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Checking frame timing is separate from keeping a stream live. If your goal is to loop uploaded videos on a YouTube channel, StreamNeo is a cloud service: upload a recording or build a playlist, add your YouTube stream key, and go live. Nothing has to stay on at home; videos stream as uploaded, up to 4K 60fps, at one price per slot, and StreamNeo automatically recovers if YouTube drops the stream. Your first day is free with no card. Monthly: $9.99 per month. See StreamNeo or start the free day.
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