How do I re-encode MP4 to FLV without quality loss?
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Upload your MP4 file and our converter applies a CRF-based re-encode targeting visually-lossless FLV output (CRF 18 by default, lower = larger / higher quality). The codec is chosen to match the FLV container (H.264 / H.265 / VP9 / AV1 as appropriate).
Which codec does the FLV output use?
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It depends on the container. MP4 defaults to H.264 (broadest playback support); MKV and WebM default to H.265 and VP9 respectively for better compression at the same quality. You can override codec choice in the advanced options before conversion.
Will my audio track survive MP4 to FLV conversion?
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Yes — audio is re-muxed (when MP4 and FLV share an audio codec) or re-encoded to AAC / Opus / Vorbis depending on what the FLV container supports. Multi-track audio (commentary, alternate languages) is preserved.
Can I keep the original framerate when converting MP4 to FLV?
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By default, framerate is unchanged (MP4 24fps stays 24fps in FLV). If you need to change it (e.g. interlaced 29.97 → progressive 30fps), use the framerate option, which handles 3:2 pulldown and deinterlacing in the same pass.
What is the file size difference between MP4 and FLV?
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Same-codec re-muxes (e.g. MP4 → FLV where both use H.264) produce nearly-identical sizes. Codec changes can swing the size dramatically: H.264 → H.265 typically halves the file at the same visual quality; H.264 → VP9 is roughly comparable.
Will the FLV file play on iPhone / Android / Smart TV?
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MP4 / H.264 plays natively everywhere. MOV / H.264 plays on Apple devices and most Smart TVs but not on older Android. MKV needs VLC on iOS. The advanced options include a "device compatibility" preset that picks the safest codec / container combination for the target device.
How long does converting a 1-hour MP4 file to FLV take?
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It 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 file finishes in 18-40 minutes.
What is the max resolution supported for MP4 to FLV?
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Up to 8K (7680×4320) on Premium. Free users are capped at 4K (3840×2160) per the file-size limit. HDR metadata (HDR10, Dolby Vision) is preserved where both MP4 and FLV containers support it.
Is my MP4 video private during conversion?
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Yes — uploaded video files are processed in isolated workers and deleted within minutes of completion. We never view, store, retain, or share content. See /privacy/ for the full data retention window.
Can I crop or trim during the MP4 to FLV conversion?
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Not in the same step — use /video-trim/ or /video-cutter/ to trim before converting, then queue the MP4 → FLV step. Trimming and converting in series is faster than re-encoding the whole file just to crop.
Why is the FLV file blurry / pixelated 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 lower-bitrate FLV at the default CRF compresses heavily on motion-heavy scenes. Push CRF down to 16-18 (or set explicit bitrate) and re-run to recover quality.
Does the MP4 to FLV converter support subtitles?
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Yes — embedded subtitle tracks (mov_text in MP4, SRT/ASS in MKV) are preserved when both MP4 and FLV containers support them. Burned-in (hardsub) subtitles transfer automatically because they are part of the video frame.