Fix Video Duration
Upload a clip whose duration is missing, Infinity, or wrong and rebuild its container locally with stream copy. The audio and video are copied unchanged — only the duration metadata is repaired.
About this tool
Use this tool when a video plays fine but its duration is missing, shows as
Infinity, jumps to 0:00, or is simply wrong. This is common with clips
recorded by the browser MediaRecorder API, screen recorders, and interrupted
downloads: the packets are intact but the container header never got a correct
duration written to it.
The fix is a remux — ffmpeg reads every packet with stream copy (-c copy)
and writes a brand-new container header with the real duration and index. Because
nothing is decoded or re-encoded, the audio and video are copied bit-for-bit and
there is no quality loss. Everything runs locally in your browser; the file is
never uploaded.
Worked example
Upload a screen-recording capture.webm whose duration reads as Infinity,
leave Output container on keep, tick Regenerate timestamps, and
download capture-duration-fixed.webm. The rebuilt file reports its true length
(for a two-second clip, ffprobe now shows duration=2.028000 instead of
N/A), while the VP9/Opus streams are unchanged.
To make a web-ready file at the same time, choose Output container = mp4 and
keep Web fast-start on: the moov atom (the index that holds the duration) is
moved to the front of the file so players and websites read the correct length
immediately and the clip streams progressively.
Options
- Output container —
keeprebuilds the same container as your input and is the safest lossless choice.mp4,mkv,mov, andwebmremux into that container instead. This is stream copy, so the codecs must fit the container (H.264/H.265/AAC → mp4/mov/mkv; VP8/VP9/Opus → webm/mkv/mp4).mkvis the most tolerant target. - Web fast-start — MP4/MOV only. Moves the index to the front of the file
(
-movflags +faststart) for progressive playback and immediate duration reads. It is ignored for mkv/webm. - Regenerate timestamps — adds
-fflags +genptsto rebuild missing or broken presentation timestamps before remuxing. Turn this on when the duration isInfinity,0:00, orN/A.
Limits and edge cases
- Maximum input size is 64 MB (browser-local processing).
- This is a container repair, not a transcode: it cannot change resolution, bitrate, or codec, and it cannot recover a truly corrupt/incomplete stream.
- Remuxing into a container the codec doesn't support (e.g. H.264 into
webm) fails by design — usekeepormkvfor the safest path. - If a file has genuinely no timestamps at all, the recomputed duration is derived from the packet count and frame rate and may differ from the original intended length by a frame or two.
FAQ
Why does my recorded WebM say the duration is Infinity?
Recorders that use the browser MediaRecorder API write the file header before
they know how long the recording will be, so the duration field is left empty and
players report Infinity. Remuxing reads the actual packets and writes the real
duration into a fresh header, which is exactly what this tool does — enable
Regenerate timestamps for these files.
Does fixing the duration reduce quality?
No. The remux uses stream copy (-c copy), so the encoded audio and video packets
are copied unchanged into a new container. Nothing is decoded or re-encoded, so the
result is bit-for-bit identical apart from the corrected container metadata.
What is "web fast-start" and when should I use it?
MP4 and MOV files store an index called the moov atom. If it sits at the end of
the file, a browser must download the whole file before it knows the duration or
can seek. Fast-start (-movflags +faststart) rewrites the file with that index at
the front, so websites can play and scrub it progressively. It only applies to
MP4/MOV output.
Can I change the exact duration to a specific value?
No. This tool repairs the duration to match the real content by rebuilding the container; it does not let you set an arbitrary duration. Setting a made-up length without re-encoding would either truncate the stream or desynchronize audio and video, so it is intentionally out of scope.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool video-duration-fix-remux 'url=https://example.com/input' 'container=keep' 'faststart=true' 'regen_timestamps=true'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/video-duration-fix-remux/?url=https://example.com/input&container=keep&faststart=true®en_timestamps=trueMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.