How do I re-encode 3GP to MKV without quality loss?
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Upload the 3GP file and our converter applies a CRF-based re-encode targeting visually-lossless MKV output (CRF 18 by default, lower = larger / higher quality). The codec is chosen to match the MKV container — H.264 / H.265 / VP9 / AV1 as appropriate.
Which codec does the MKV output use?
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It depends on the container. MP4 defaults to H.264 (broadest playback support); MKV defaults to H.265 for ~50% smaller file at the same quality; WebM defaults to VP9 or AV1 (royalty-free web streaming). You can override the codec choice in the advanced options before MKV conversion runs.
Will my audio track survive 3GP to MKV?
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Yes — audio is re-muxed when 3GP and MKV share an audio codec, or re-encoded to AAC / Opus / Vorbis depending on what the MKV container supports. Multi-track audio (commentary, alternate languages) is preserved in containers that support it (MKV, WebM, MP4).
Can I keep the original framerate going from 3GP to MKV?
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By default framerate is unchanged (3GP 24fps stays 24fps in MKV). If you need to change it (e.g. interlaced 29.97 to progressive 30fps) the framerate option handles 3:2 pulldown and deinterlacing in the same pass — no second decode required.
What is the file size difference between 3GP and MKV?
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Same-codec re-muxes (H.264 in both 3GP and MKV) produce nearly-identical sizes. Codec changes can swing things dramatically: H.264 -> H.265 typically halves the file at the same visual quality; H.264 -> VP9 is roughly comparable; AV1 is currently the smallest at the cost of slower encode time.
Will the MKV file play on iPhone / Android / Smart TV?
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MP4 / H.264 plays everywhere natively. MOV / H.264 plays on Apple devices and most Smart TVs but not on older Android. MKV needs VLC on iOS. WebM plays in browsers but not most Smart TV apps. The "device compatibility" preset in advanced options picks the safest codec / container for your target.
How long does converting a 1-hour 3GP file to MKV take?
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Depends on the codec change. Same-codec re-mux: 30-60 seconds (no re-encode). Re-encode to a different codec: typically 0.3-0.7x source duration on our GPU pipeline, so a 1-hour 3GP -> MKV finishes in 18-40 minutes; AV1 re-encodes are 2-3x slower.
What is the max resolution supported for 3GP to MKV?
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Up to 8K (7680x4320) on Pro. Free is capped at 4K per the file-size limit. HDR metadata (HDR10, Dolby Vision) is preserved where both 3GP and MKV containers and codecs support it; SDR sources stay SDR.
Is my 3GP video private during MKV conversion?
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Yes — uploaded video files are processed in isolated workers and deleted within minutes of completion. No human review, no retention beyond the documented window. See /privacy/.
Can I crop or trim during the 3GP to MKV step?
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Not in the same step — use /video-trim/ or /video-cutter/ to clip the 3GP first, then queue the 3GP -> MKV conversion. Trim-then-convert is faster than re-encoding the whole file just to crop the output.
Why is the MKV file blurry compared to the 3GP source?
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Almost always a bitrate-too-low setting. Re-encoding a high-bitrate 3GP into a lower-bitrate MKV at the default CRF compresses motion-heavy scenes heavily. Push CRF down to 16-18 (or set an explicit bitrate ceiling) and re-run to recover quality.
Does the 3GP to MKV converter support subtitles?
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Yes — embedded subtitle tracks (mov_text in MP4, SRT / ASS in MKV, WebVTT in WebM) are preserved when both 3GP and MKV containers support them. Burned-in (hardsub) subtitles transfer automatically because they are part of the pixel data.