usefulweb.site Universal Video Converter

Audio, video & images

Universal Video Converter

Convert video to MP4, WebM, MOV or MKV: resize, set quality and fps, or remux losslessly.

MP4, MOV, MKV, WebM, AVI, MPEG-TS, WMV, FLV; max 250 MB and 20 minutes. Processed on our server in a private temporary folder that is deleted afterwards; the result can be downloaded for about 2 hours.

Overrides the quality preset. Lower = better and larger. H.264: 0–51 (18–28 typical); VP9: 0–63 (24–40 typical).

Caps the short side (height for landscape, width for portrait). Never enlarges.

Try an example: MP4 test clip to WebM (VP9/Opus) · Remux MP4 into MKV without re-encoding

How it works

Converts MP4, MOV, MKV, WebM, AVI and other videos to MP4 (H.264/AAC), WebM (VP9/Opus), MOV or MKV. Cap the resolution, choose the quality (CRF) and frame rate, and keep the audio as is when the target container supports it. Remux-only mode changes the container without re-encoding when the codecs fit — fast and lossless.

  • The container is detected from the file content and ffprobe reads codecs, resolution, frame rate, rotation and duration.
  • Remux mode copies the first video stream and all audio streams (-c copy) when the target container accepts the codecs (MP4/MOV: H.264, HEVC, AV1, VP9, MPEG-4 + AAC, MP3, AC-3, Opus, FLAC; WebM: VP8, VP9, AV1 + Opus, Vorbis; MKV: almost anything). Nothing is re-encoded, so quality is identical.
  • Re-encoding uses libx264 (preset veryfast, CRF, High profile, yuv420p) for MP4/MOV/MKV or libvpx-vp9 (constant quality CRF, cpu-used 5, row-mt) for WebM, with -threads 2 on our 2-vCPU server. Scaling keeps the aspect ratio with even dimensions and never enlarges; the frame rate is only ever reduced.
  • Audio is copied when the target container supports the codec, otherwise encoded as AAC 128 kbit/s (MP4/MOV/MKV) or Opus 96 kbit/s (WebM). Subtitles and data tracks are dropped.
  • Before encoding, the work is estimated from output pixels × frames; jobs that would exceed about 220 s of encoding are refused with a suggestion (lower resolution/fps, trim, or remux).

Sources

For scripts and AI agents

  • JSON API: POST https://videoconverter.usefulweb.site/api/v1/calculate (same calculation as this page)
  • Interface description: OpenAPI 3.1 · AI guide: llms.txt
  • MCP server (Streamable HTTP): https://videoconverter.usefulweb.site/mcp · tool name video_converter
Example request
curl -s -X POST https://videoconverter.usefulweb.site/api/v1/calculate \
  -H 'content-type: application/json' \
  -d '{…see OpenAPI examples…}'

Related tools

  • Video Compressor – Shrink a video to a target size (two-pass) for e-mail, WhatsApp or Discord, or by quality.
  • Video Cutter & Merger – Trim video, remove a section or join clips: lossless copy or frame-exact re-encode.
  • Video to MP3 Extractor – Extract a video’s soundtrack as MP3, WAV or FLAC, or copy the original audio losslessly.
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