Convert Video Format

About Video Format Converter

This online tool allows you to convert video files between different formats directly in your browser. Perfect for compatibility, optimization, or platform requirements. Convert MP4 to WebM for web, MOV to MP4 for universal playback, or optimize video size and quality. All processing happens locally for complete privacy.

What's the difference between a container and a codec?

A container (also called a wrapper or format) is the file format that holds the streams: MP4, MKV, WebM, MOV, AVI. A codec (encoder/decoder) is the algorithm that compresses the video or audio inside: H.264, H.265, VP9, AV1 for video; AAC, Opus, MP3, FLAC for audio. So an .mp4 file might contain H.264+AAC or H.265+AAC. Two files with the same .mp4 extension can be totally different inside, which is why some MP4s play everywhere and others fail on older devices. This converter changes the container and can also re-encode the streams to a different codec. If you only need to change the wrapper (for example MKV to MP4) without re-encoding, that is called remuxing and is nearly instantaneous because no decoding happens.

Why won't my MP4 play on this device even though it's MP4?

MP4 is just the container; the codec inside is what matters for compatibility. Most older smart TVs, default media players, and chat apps only decode H.264 Baseline or Main Profile at up to Level 4.1. If your MP4 has H.265 (HEVC), VP9, or AV1 video, or AAC at a sample rate outside 44.1/48 kHz, playback fails silently or shows audio-only/video-only. Other gotchas: 10-bit color (High10), B-frames in Baseline-only decoders, Main10 HEVC instead of Main, or DTS audio instead of AAC. Converting to MP4 + H.264 (yuv420p, 8-bit) + AAC LC stereo at 48 kHz fixes ~99% of these problems and is the safest interchange format for anything from email to digital signage.

Does converting between formats reduce quality?

It depends on whether the conversion re-encodes the video. Remuxing (changing only the container, e.g. MKV to MP4 with -c:v copy -c:a copy in FFmpeg) is lossless because the encoded streams are copied byte-for-byte. Transcoding (changing the codec, e.g. H.264 to H.265) re-decodes and re-encodes, which always loses some quality even at high CRF settings because lossy codecs throw away information at every encode. To minimize loss when transcoding, use a high-quality setting (CRF 18-20), avoid converting between similar lossy codecs unless necessary, and never convert through a chain like H.264 to MP3-audio-only to AV1 — each step degrades the result. When in doubt, keep the original source file.

Which format should I pick for social media uploads?

Most platforms (Instagram, TikTok, YouTube, X/Twitter, Facebook) require or strongly prefer MP4 with H.264 video + AAC audio. Recommended specs: H.264 High Profile, Level 4.2 or lower, yuv420p 8-bit color, 30 or 60 fps (constant), keyframe every 2 seconds, AAC-LC stereo at 128-192 kbps, 48 kHz sample rate. Resolutions: 1080x1920 vertical for Reels/TikTok/Shorts, 1080x1080 square, 1920x1080 horizontal. The platforms re-encode your upload anyway, so don't waste bitrate above ~12 Mbps for 1080p or ~50 Mbps for 4K — the source quality has to be good enough to survive their re-encode, not match it. WebM or MKV files are usually rejected at upload.

What is the best format for archival or long-term storage?

For genuine archival (preserve every pixel), use a lossless codec like FFV1 or ProRes in an MKV or MOV container, with FLAC or PCM audio. FFV1 is open, royalty-free, and used by the Library of Congress for film preservation. For practical archival with strong compression, H.265 (HEVC) Main10 at CRF 18-20 in MKV with FLAC audio is a good balance — roughly 30-50% of the original size with visually lossless quality and 10-bit precision that prevents banding over time. Avoid MP4 for archival because MKV is more forgiving of mixed streams, attachments, chapters, and subtitles. Always keep at least two copies on independent physical media, and migrate to a current format every 5-10 years as codec ecosystems shift.

Can I convert without re-encoding (stream copy / lossless)?

Yes, if the source and target containers both support the existing codecs. This is called remuxing, in FFmpeg done with -c:v copy -c:a copy. It is nearly instant because no decoding happens — only the container metadata is rewritten. Common safe remuxes: MKV to MP4 (when video is H.264/H.265 and audio is AAC), MOV to MP4 (usually identical codecs), TS to MP4 (broadcast streams). Remuxing fails or requires fallback when the codec is unsupported by the new container (Vorbis in MP4, Opus in older MP4 specs, ProRes in MP4) or when the bitstream needs filtering (e.g., extracting Annex B H.264 from MPEG-TS and converting to the AVCC format MP4 expects). When remuxing works, it is the gold standard for format conversion: zero quality loss, seconds to complete.

How do MP4, MKV, MOV, AVI, and WebM differ?

MP4 (ISO/IEC 14496-14, derived from QuickTime) is the universal interchange format, supported by every device and platform but with stricter codec rules. MKV (Matroska, open source) is the most flexible: supports any codec, multiple audio/subtitle tracks, chapters, attached fonts and cover art. Ideal for movies and ripped Blu-rays. MOV (Apple QuickTime) is essentially identical to MP4 structurally and often interchangeable, but is the native format for Final Cut Pro and supports ProRes intermediate codecs. AVI (Microsoft, 1992) is legacy: it lacks proper streaming support, can't handle modern codecs efficiently, and should be avoided for new content. WebM (Google subset of Matroska) is the open-web standard for VP8/VP9/AV1 video and Opus audio, optimal for HTML5 video embedding.

Does the file extension actually matter, or just the contents?

Both, but for different reasons. Internally, players inspect the first bytes (magic number) and metadata to identify the actual container format, so renaming film.mp4 to film.mkv won't break a smart player that does its own format sniffing. However, operating systems route files to apps based on extension, web servers send MIME types based on extension, browsers refuse to play files served as wrong MIME, and many older or simpler players trust the extension exclusively and will refuse a misnamed file. So if you remux MKV content into an MP4 container, save it as .mp4 to match. Conversely, never just rename — that does not change the container. Use a proper converter (or FFmpeg with -c copy) to actually remux.