How to split a big video file to fit a FAT32 USB stick (or avoid splitting at all)
The film is 7 GB, the stick says it has 30 GB free, and Windows still says the file is too large. That's FAT32's 4 GB file limit, and you have three good ways round it.
Which way round the limit?
| Goal | Best option | Quality |
|---|---|---|
| Watch on a TV, car screen or player that reads exFAT | Reformat the stick as exFAT and copy the file as it is | Untouched |
| Watch on a device that only reads FAT32 | Split into playable parts with ffmpeg (below) | Untouched, a few seconds' overlap or gap at the joins at most |
| Want a single file for a FAT32-only device | Re-encode it smaller, under 4 GB | Some loss, usually hard to see at sensible sizes |
| Just moving it to another computer | Split into chunks with 7-Zip or split, rejoin later | Untouched, but the chunks won't play until rejoined |
Split into playable parts with ffmpeg
ffmpeg is a free command-line video tool for Windows, Mac and Linux. With -c copy it cuts the file without re-encoding, so it takes seconds and keeps the original quality:
ffmpeg -i film.mp4 -c copy -map 0 -f segment -segment_time 1800 -reset_timestamps 1 film-part%02d.mp4-segment_time 1800is the part length in seconds (1800 = 30 minutes).-map 0keeps every audio and subtitle track, not just the first.-reset_timestamps 1makes each part start at 0:00, which some TVs need.- ffmpeg can only cut at a keyframe, so parts can be a few seconds longer than asked. That's why you leave a margin under 4 GB.
- For an MKV, keep the extension:
film-part%02d.mkv.
Working out the part length
A file's size is its bitrate times its length. Work out the average bitrate, then how many seconds fit in about 3,900 MB (safely under the 4,096 MB limit):
- Bitrate (Mbit/s) = size in MB × 8 ÷ length in seconds. A 10,000 MB film of 2 hours (7,200 s): 10,000 × 8 ÷ 7,200 ≈ 11.1 Mbit/s.
- Seconds per part = 3,900 × 8 ÷ bitrate. Here 31,200 ÷ 11.1 ≈ 2,810 s, about 46 minutes.
- So
-segment_time 2700(45 minutes) gives three parts of roughly 3.8 GB, 3.8 GB and 2.4 GB.
The video size calculator does this for you and also gives the bitrate for shrinking the film under 4 GB in one piece.
Shrink it under 4 GB instead
A two-hour film at 1080p usually looks fine at 4 GB, which is about 4.2 Mbit/s for the video plus the sound. Re-encoding takes a while (often as long as the film or longer on a laptop) and loses a little detail. A two-pass encode lands closest to the target: the compress a video to a target size guide has the exact commands.
Split just for carrying, then rejoin
- 7-Zip (Windows): right-click the file, 7-Zip, Add to archive, set "Split to volumes" to
4000Mand the compression level to Store (video doesn't compress further). At the other end, open the.001file with 7-Zip and extract. - Mac or Linux:
split -b 4000m film.mp4 film.mp4.part-makes chunks, andcat film.mp4.part-* > film.mp4joins them again. - Windows, joining without 7-Zip:
copy /b film.mp4.part-aa + film.mp4.part-ab film.mp4in Command Prompt, listing the parts in order.
These chunks are just slices of bytes, so a TV can't play them. Use ffmpeg's segment option if you want to watch the parts.
Related
Why cuts without re-encoding can start blocky · "File too large for the destination file system" · Which format for a USB stick for a TV, car or console · Compress a video to a target size · Video size calculator · What is exFAT?
Questions
How do I split a video into parts without losing quality?
Use ffmpeg with -c copy and the segment muxer, for example: ffmpeg -i film.mp4 -c copy -map 0 -f segment -segment_time 1800 -reset_timestamps 1 film-part%02d.mp4. It cuts at keyframes without re-encoding.
How long should each part be to stay under 4 GB?
Divide about 3,900 MB times 8 by the video's bitrate in Mbit/s. For an 11 Mbit/s film that's about 2,800 seconds, so 45-minute parts are safe.
Can I copy a file over 4 GB to FAT32 at all?
No, FAT32 can't store any single file of 4 GB or more. Split it, shrink it, or reformat the drive as exFAT or NTFS.
Will my TV play the parts made by 7-Zip or split?
No. Those are raw slices that only work after being joined back together. For playable parts, use ffmpeg's segment option.
Is it better to split or to reformat the stick as exFAT?
If the TV or player reads exFAT, reformatting is simplest: one file, no editing. Splitting is for devices that only read FAT32.
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