Step 1: Transfer your MP4 files using the button above or by slide and deposit.
Step 2: Click the 'Convert' button to start the conversion.
Step 3: Retrieve your converted WebM files.
MP4 to WebM Conversion FAQ
How do I re-encode MP4 to WebM without losing video quality?
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Upload your MP4 file and the converter runs a CRF-based re-encode targeting visually-lossless WebM output (CRF 18 by default, lower values = larger file / higher quality). The codec is chosen to match the WebM container — H.264 for broad-compat MP4, H.265 for size-efficient MKV, VP9 for WebM, AV1 for newer pipelines. Almost every MP4 in the wild is H.264 video with AAC audio; the container also legally holds HEVC, AV1 and VP9. WebM is deliberately narrow: VP8 or VP9 video (AV1 more recently) with Vorbis or Opus audio, and nothing else.
Both MP4 and WebM are modern containers — which should I actually keep?
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Keep whichever matches where the file is going, because neither is better in the abstract. One of these two is built for playback compatibility and the other for holding everything a file might contain, and they trade against each other exactly along that line. The pragmatic answer for most libraries is to archive in the feature-rich container and export to the compatible one on demand. MP4 is the safest possible delivery target — every phone, browser, console, editor and Smart TV built in the last decade plays it without extra software. WebM plays natively in every modern browser with no plugin, no licence fee and no patent exposure, which makes it the default for web-embedded video.
Which video codec does the WebM output use?
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It depends on the WebM container. MP4 defaults to H.264 for the broadest playback support across phones, browsers, and Smart TVs. MKV defaults to H.265 / HEVC for roughly half the file size at equivalent quality. WebM defaults to VP9. The advanced options expose explicit codec choice if you need to override. WebM is a strict subset of Matroska that Google published in 2010 specifically to give HTML5 video a royalty-free container.
Will my audio track survive MP4 to WebM conversion?
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Yes. When MP4 and WebM share an audio codec (e.g. both carry AAC), audio is re-muxed with no re-encode — bit-identical. When the codecs differ, audio is transcoded to AAC / Opus / Vorbis depending on what the WebM container supports. Multi-track audio (commentary, alternate languages) is preserved.
Can I keep the original framerate when converting MP4 to WebM?
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By default yes — a 24fps MP4 stays 24fps in WebM; a 60fps MP4 stays 60fps. If you need to change rate (e.g. interlaced 29.97 → progressive 30, or 60 → 30 for upload limits), the framerate option handles 3:2 pulldown, deinterlacing, and frame-blending in the same encode pass.
How much will the file size change going from MP4 to WebM?
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Same-codec re-mux (MP4 H.264 → WebM H.264 just changing container): nearly identical size. Codec change can swing dramatically: H.264 → H.265 typically halves the file at the same visual quality; VP9 is roughly comparable; AV1 cuts another 20-30% but is slower to encode.
Will the WebM file play on iPhone, Android, and Smart TVs?
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MP4 / H.264 plays natively on every modern device. MOV / H.264 plays on Apple devices and most TVs but not always on older Android. MKV needs VLC on iOS. WebM is browser-first. The advanced options include a "device compatibility" preset that picks the safest WebM codec / container for your target. WebM is a poor fit anywhere outside a browser — video editors, phones’ native galleries and Smart TVs largely ignore it.
How long does converting a 1-hour MP4 video to WebM take?
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Same-codec re-mux is near-instant — 30 to 60 seconds for a 1-hour file. A full codec re-encode runs at roughly 0.3-0.7x source duration on our GPU pipeline, so a 1-hour MP4 → WebM finishes in 18-40 minutes depending on resolution and target codec.
What is the maximum resolution supported for MP4 to WebM?
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Up to 8K (7680×4320) on Premium plans. Free conversions are capped at 4K (3840×2160) by the per-file size limit. HDR metadata (HDR10, HDR10+, Dolby Vision when present) is carried through where both MP4 and WebM containers support it.
Is my MP4 video private during conversion to WebM?
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Yes. Uploaded video files are processed in isolated workers, never viewed by a human, never indexed, and deleted within minutes of completion. The retention window is documented at /privacy/ and we publish no training corpus from user uploads.
Can I crop, trim, or rotate during the MP4 to WebM conversion?
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Not in the same step — use /video-trim/ or /video-cutter/ to clip first, then run the MP4 → WebM conversion. Chaining trim and convert is faster than re-encoding the entire MP4 just to drop unused footage.
Why is the WebM file blurry compared to the MP4 source?
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Almost always a bitrate-too-low setting. Re-encoding from a high-bitrate MP4 into a default-CRF WebM compresses heavily on motion-rich scenes. Push CRF down to 16-18, or set an explicit target bitrate matched to the MP4 source, and the WebM regains its clarity.
