MP4 to MP4 Converter

How to Re-encode an MP4 Online

1. Upload Your MP4 File: Drag and drop or click "Add Files" to select MP4 or M4V videos. Batch is supported — all files run with the same settings.
2. Pick Video Codec and Audio Codec: Default is H.264 + AAC, which plays on virtually every device made since 2010. Switch Video Codec to H.265 (HEVC) to cut size roughly 25-50% at the same quality, or AV1 for the smallest output on modern hardware. Leave Audio Codec on AAC for compatibility, or pick MP3 for legacy players.
3. Choose File Compression Mode: Pick Quality Preset (Very High is the default; step down to High, Medium, or Low to shrink), Target File Size as % (slider 1-100%), Specific File Size in MB/KB (e.g., 25 MB for email), Constant Bitrate / Variable Bitrate for streaming targets, or Constant Quality (CRF) — CRF 18 is visually lossless, 23 is the H.264 sweet spot, 28 is small-and-shareable.
4. Adjust Video Resolution, Trim, then Convert: Keep original, drop to a preset (4K, 1440p, 1080p, 720p, 480p, 360p), scale by percentage, or enter custom Width × Height. Use Trim → Time Range to set Start Time and Duration if you want a clip. Click Convert. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after one hour — no sign-up, no watermark, never shared.

Why Re-encode an MP4?

MP4 is a container, not a codec. A "4K HEVC MP4 from an iPhone" and a "1080p H.264 MP4 from a screen recorder" share the same .mp4 extension but are very different files. Re-encoding lets you change what's inside the container — the video codec, audio codec, bitrate, resolution, or duration — without changing the format your destination expects. Files are uploaded over an encrypted connection, processed on xconvert's servers, and deleted automatically after one hour.

• Make an HEVC iPhone clip play on older devices — iPhones since the iPhone 7 (iOS 11, 2017) record in HEVC by default. Re-encode to H.264 + AAC so a 2014-era Android, a Windows 10 PC without the HEVC extension, or a hotel TV via USB can play it.
• Hit a strict upload cap — X (Twitter) caps non-Premium uploads at 512 MB and 2:20 in length, Discord's free tier caps attachments at 10 MB, and Gmail caps attachments at 25 MB. Specific File Size mode lets you target the exact ceiling instead of guessing at bitrates.
• Shrink a 4K master for editing or sharing — A 10-minute 4K HEVC clip can be 2-4 GB. Dropping to 1080p H.264 at CRF 23 typically yields 200-400 MB while staying visually clean on phones, tablets, and most TVs.
• Standardize a folder of mixed MP4s — Drag in clips from a phone, a drone, a screen recorder, and a DSLR; pick one codec + resolution + bitrate; export a clean uniform set ready for a timeline in Premiere, Resolve, or CapCut.
• Trim without re-wrapping — Set a Time Range to extract a 30-second highlight from a 90-minute capture; the rest of the file is discarded in the same pass.
• Switch to AV1 for archiving — AV1 is royalty-free and gives roughly 30% better compression than H.265 at the same quality, useful when you're storing long-term and don't need maximum device compatibility today.

H.264 vs H.265 vs AV1 — Codec Comparison

CRF and File-Size Quick Guide

Frequently Asked Questions

Why does my MP4 not play on my older device when it works on my phone?

Almost always a codec mismatch. An iPhone records HEVC (H.265) MP4 by default; an older Android, a Smart TV from before ~2017, or a stock Windows 10 install without the HEVC Video Extension can't decode it. Re-encode to H.264 + AAC at the same resolution — you'll get a slightly larger file but it will play everywhere. The container stays .mp4; only the inside changes.

Does converting MP4 to MP4 always lose quality?

Yes, any re-encode is lossy because the source is already a lossy codec — decoding and re-encoding compounds the rounding. The loss is small when you use Constant Quality at CRF 18-20 and invisible to most viewers at CRF 23. If your only goal is to trim or rewrap and the source codec is already what you want, you can use Trim MP4 to cut without a full re-encode in many cases.

Should I pick H.264, H.265, or AV1?

Pick H.264 when you need the file to "just work" — email attachments, sharing with non-technical people, playback on a TV via USB, embedding in old PowerPoints. Pick H.265 when the destination is iPhone, Mac, Apple TV, a modern Smart TV, or your own archive and you want files ~40% smaller. Pick AV1 when the destination is web streaming (YouTube, Netflix), a modern Chromium browser, or long-term storage and you can wait through the slower encode.

What's the difference between CRF and Target File Size?

CRF (Constant Rate Factor) fixes the visual quality and lets the encoder pick whatever bitrate is needed — predictable quality, unpredictable size. Target File Size fixes the output size and lets the encoder lower bitrate (and quality) until the file fits — predictable size, variable quality. Use CRF when you care about how the video looks; use Target File Size when you need to hit a 25 MB email cap or a 10 MB Discord limit.

How do I shrink a 4K iPhone clip enough to email?

A 1-minute 4K HEVC iPhone clip is typically 150-400 MB. To fit Gmail's 25 MB cap: set Video Resolution to 1080p (or 720p for stronger reduction), keep Video Codec on H.265, and use Specific File Size = 25 MB. If you need the recipient to play it without HEVC support, switch to H.264 — the file will be slightly larger so you may need to drop to 720p as well.

Can I change just the audio codec without re-encoding the video?

This tool re-encodes both tracks in a single pass. If the video codec is already what you want, set Quality Preset to Very High and the visible loss will be minimal — but the video is still being decoded and re-encoded. True stream copy (mux without re-encoding) requires a remux tool; xconvert's pipeline always re-encodes when you select a codec.

Will my video metadata, rotation flag, and creation date survive?

Container-level metadata like rotation, creation date, and most title/artist tags are preserved. Custom or vendor-specific atoms (iPhone slow-motion ramp data, GoPro telemetry, DJI flight metadata) are typically dropped because they're not part of the standard MP4 spec. If you need those, edit a copy and keep the original.

What's the largest MP4 I can re-encode in the browser?

processing runs on our servers, so the practical ceiling is upload size and connection speed and how long you're willing to leave the tab open — typically 2-4 GB on a desktop with 16 GB RAM, less on mobile. For multi-hour 4K masters, expect minutes to tens of minutes of encode time depending on your CPU. files are uploaded over an encrypted connection and auto-deleted after one hour.

Can I do MP4 to MP4 in batch?

Yes — drop in multiple MP4 or M4V files and a single set of options applies to all of them. Each file is processed independently in the same session, so a failure on one doesn't block the others. If you also need to compress aggressively rather than re-encode, Compress MP4 exposes the same engine with compression-focused defaults.