Video to MP4 Converter: Turn Short Clips Into H.264 and AAC
Changing a filename from .webm to .mp4 does not convert the video inside it. A playable MP4 needs compatible streams in the MP4 container. This tool decodes your short source clip and makes a new H.264 video stream, then converts its first audio stream to AAC when audio is present. Choose a MOV, WebM, MKV, AVI, or MP4 file above and select the output quality. The browser renders and downloads the result locally. There is no account, upload queue, or server-side copy of your video.
Input containers are not the same as video codecs
MP4, MOV, WebM, MKV, and AVI describe ways to package streams. Each may contain a different video or audio codec. A WebM file might use VP8 or VP9 video, for example, while an MP4 might contain H.264 or HEVC. The tool reads the streams with FFmpeg before it starts encoding. A supported filename extension does not guarantee that the particular video or audio codec inside your file can be decoded by this ffmpeg.wasm build. If inspection or decoding fails, try another source file rather than renaming the extension.
The FFmpeg format documentation separates containers and demuxers from the codecs used inside them. The FFmpeg codec documentation covers encoding and decoding separately. This converter produces MP4 only. It does not export GIF, MOV, WebM, or uncompressed AVI. If you need WebM as the finished format, use a different workflow.
File size, dimensions, and duration limits
A source file can be at most 100 MB and three minutes long. Its video must fit inside a 1920 x 1080 pixel budget, including vertical video with the sides reversed. The file must contain a readable video stream with a frame rate of 60 fps or lower. The converter checks these properties in the browser after loading the encoder. It rejects unsupported files rather than starting an unbounded transcode. Files that are within these limits can still fail on a phone with little free memory. A 100 MB source must coexist with decoded frames and the new output while the browser works.
Output fits within 1280 x 720 pixels without stretching the source shape. A 1080 x 1920 portrait clip becomes about 404 x 720 pixels after even-dimension rounding. A 640 x 360 clip stays close to its original dimensions instead of being enlarged. Video over 30 fps is reduced to 30 fps. A 24 fps film clip stays at its original rate. The browser encodes with H.264 and uses 8-bit 4:2:0 output pixels. Expect some loss of detail even on the Higher quality setting.
Quality choices and when size matters
Smaller file uses CRF 34 with 96 kbps AAC audio. Balanced uses CRF 28 and 128 kbps AAC. Higher quality uses CRF 23 and 160 kbps AAC. The setting controls how much detail the H.264 encoder may discard. It is not a target number of megabytes. For example, converting a 40 MB high-bitrate camera clip might produce a 15 MB MP4, but re-encoding a 10 MB WebM with the Higher quality setting may produce a larger file. The result panel shows the actual difference.
The first audio track is included if it exists. A silent source remains silent. Additional audio streams, subtitle streams, chapters, and source metadata are not preserved. If your input has a director's commentary track or embedded captions, keep the original. Check whether the MP4 plays on your target device and listen through the end. No browser converter can promise identical playback on every app or social platform.
Choose the right task before transcoding
If you already have H.264 in an MP4 and only want to reduce its size, try the MP4 video compressor. It reports the measured size reduction and refuses other input codecs. If you have music and cover art but no footage, the image plus audio video makermakes a still-image MP4 from one or more songs. Neither tool changes the video format back to the source after export.
Need to prepare a soundtrack first? The audio format converterhandles audio files on their own. The sample rate calculator explains why raw audio can occupy far more space than a compressed soundtrack. For a clip timed to a beat, use the music time converterto work out bars and seconds before recording. These tools solve different problems, so use the one that matches your source files.
On first use, your browser downloads the ffmpeg.wasm encoder. Your video is not sent with that download. H.264 encoding uses the device's processor and may run slower than real time. Close other demanding tabs, start with a short clip, and leave this tab open until the MP4 preview appears. You can cancel an active job. If the new MP4 is larger than the source, the result panel says so; re-encoding alone does not guarantee a smaller file.
