The best balance of speed, smaller file size, and minimal quality loss for re-encoding a big MP4 is using FFmpeg with hardware-accelerated H.265/HEVC (or AV1 on newer hardware).
This is far superior to basic online compressors or simple bitrate reduction.


Recommended Approach: FFmpeg (Free, Powerful, Fastest with Hardware)

FFmpeg is the gold standard, it's what powers most GUI tools under the hood. HandBrake is a good user-friendly alternative with a GUI if you prefer that.


1. Fastest Option: Hardware Acceleration (NVENC, Quick Sync, etc.)

Use your GPU/CPU's dedicated encoder for 5-10x faster speeds than pure CPU encoding, with very good quality.

NVIDIA GPU (RTX 20xx or newer recommended): hevc_nvenc (H.265)
Intel CPU (recent integrated graphics): hevc_qsv
AMD: hevc_amf

Best fast command for minimal quality loss (H.265 NVENC example):

-cq 24: Quality-based (lower = better quality/larger file; 20-28 range is good "visually near-lossless" for most content). Adjust based on your source.
-preset p5 or p4-p7: Balances speed/quality (higher = slower/better compression).
-c:a aac -b:a 128k: Compresses audio lightly (or use -c:a copy to keep original if it's already good).
-movflags +faststart: Makes the video streamable (web-friendly).

For even better quality/size (still fast on good hardware): Try AV1 with av1_nvenc (RTX 40-series+) if your playback devices support it—~20-30% smaller files than HEVC at similar quality.


2. Highest Quality/Smallest Size (Slower CPU Encoding)

If you can wait longer for better compression:



-crf 24-28: Constant Rate Factor (quality mode). ~18-23 for near-visually-lossless, higher for more compression. H.265 CRF values are typically 4-6 higher than H.264 equivalents.
-preset medium (or slow/veryslow for even smaller files, much slower).

H.264 fallback (better compatibility, larger files):

Code:
ffmpeg -i input.mp4 -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 128k output.mp4

Expected Results

Size reduction: 40-70%+ smaller depending on original bitrate, resolution, and settings (HEVC/AV1 shine here vs. H.264).
Quality: CRF mode keeps it "visually lossless" or very close, test on your videofile.
Speed: Hardware = minutes for a big file; pure CPU slow preset = hours.

Other Tips for Better/Faster Results

Downscale if possible: Add -vf scale=1920:-2 (for 1080p) or similar—biggest size saver with little perceived loss on smaller screens.
Test first: Run on a short clip: ffmpeg -i input.mp4 -ss 00:05:00 -t 60 ... (skip to 5 min, encode 60 sec).
Two-pass for precise bitrate control (less common now with CRF).
GUI alternative: HandBrake — select H.265 (NVENC/Quick Sync if available), CRF ~24-28, medium/slow preset. Very similar results.
Online tools (e.g., VideoCompress, Cloudinary-based): Convenient for quick jobs but less control, potential quality hits, and privacy/upload limits. Not ideal for "big" files.

Quick Start

Download FFmpeg (static build from official site or winget install ffmpeg on Windows).
Run the command in terminal/cmd.
Compare original vs. output with VLC (side-by-side) and file sizes.

Hardware makes the biggest difference for speed. If you share your GPU/CPU, input resolution/bitrate (run ffmpeg -i input.mp4), I can refine the exact command.
AV1 is the future for ultimate efficiency if supported.