Which Video Converter for Which Job: Batch, Private, Old Formats, 4K

The four jobs, one line each

• A whole folder at once: HandBrake's queue if you want an interface, one ffmpeg loop if you do not.
• The file must not leave your machine: any desktop converter - HandBrake, VLC, ffmpeg - and no browser tool that uploads.
• Old formats (WMV, AVI, VOB, FLV): check the codec inside before choosing between a seconds-long remux and a full re-encode.
• 4K footage: decide whether you need 4K out at all; if the destination is 1080p, scale down in the same pass.

Batch: a folder, not a file

The people searching for this do not type "batch". They type how to add a folder to HandBrake's queue, or how to make ffmpeg convert every file in a directory. Both routes exist and both are free.

In HandBrake, open the folder as the source, pick one preset, then use Add to Queue with the add-all option so every title lands in the queue with the same settings, and start the queue once. Two things to know before trusting it overnight. HandBrake always re-encodes the video stream; it has no stream-copy mode, so a folder that only needs a container change is slower here than it has to be. And subtitles in a batch follow the same rules as in a single file - if the source tracks are not selected in the preset, they will be missing from every output, not just one.

On the command line, one loop covers the whole folder:

for f in *.avi *.wmv; do ffmpeg -n -i "$f" -c:v libx264 -crf 23 -c:a aac "${f%.*}.mp4"; done

The -n flag refuses to overwrite anything that already exists, which makes the loop safe to re-run after an interruption. Measured on an Apple Silicon laptop with ffmpeg 9.0.1: four 10-second 640×480 clips - three AVI, one WMV - converted in 1.8 seconds total, each output H.264 + AAC. If every file in the folder is already H.264 and only the wrapper is wrong, swap the encoder flags for -c copy and the loop becomes a remux; the MKV to MP4 remux guide covers the subtitle flag that a copy loop silently needs.

If the folder-batch job is recurring and the queue workflow is the part you would rather not learn, a paid desktop tool with drag-and-drop batches is a reasonable trade - something like Movavi's editor, which exports to MP4 and other formats without an upload step. For a one-off folder, the free routes above are enough.

Private: the file never leaves the machine

A browser converter has to upload your video to its server before it can touch a frame. That is fine for a meme clip and not fine for client footage, unreleased work, or anything with faces that did not agree to be on someone else's disk. Deletion policies are promises you cannot audit from the outside; the only converter that provably keeps the file private is one that never sends it.

Every desktop route qualifies: HandBrake, VLC's Convert/Save dialog, ffmpeg. All three run with the network cable unplugged, which is the simplest test of the claim. The one browser exception is a tool that processes inside the tab - the file is read by your own browser and never posted anywhere. The video compressor on this site works that way, for the narrower job of making a file smaller. The upload step is also what creates the free tiers' size caps, as covered in the over-1GB guide - privacy and no-ceiling come from the same design.

Old formats: read the codec before picking the route

WMV, AVI, VOB and FLV are containers, and what they carry decides the work. The local test makes the split concrete:

• AVI with Xvid video and MP3 audio: ffmpeg -i old.avi -c copy old.mp4 exited cleanly; the MP4 holds the original MPEG-4 Part 2 video and MP3 audio, untouched. VLC and most desktop players open it. If a stricter target such as an editor or a phone gallery refuses it, re-encode to H.264.
• WMV with Windows Media Video 8 (wmv2): the same copy command failed with "Could not find tag for codec wmv2" and exit code 234. MP4 has no slot for that codec, so a WMV of that vintage always needs a full re-encode - no rename, remux or "lossless" option will skip it.

To see which case you have, run ffprobe -v error -show_entries stream=codec_name -of csv=p=0 file.avi. If it prints h264 or mpeg4, try the remux first; it takes seconds and changes nothing. Anything Windows-Media, or anything the remux rejects, goes straight to -c:v libx264 -crf 23 -c:a aac. The MOV vs MP4 explainer covers why the container and the codec are two separate questions.

4K: most of the time the job is downscaling

The autocomplete around "4K video converter" is dominated by "to 1080p". People who search it usually have 4K footage and a destination that does not want it - a chat app, a slideshow, an old TV, an upload that will be downscaled anyway. Converting 4K to 4K is the expensive version of the job; scaling to 1080p in the same pass is cheaper on every axis.

Measured on a 10-second 3840×2160 synthetic test clip (45.8 MB), libx264 CRF 23, preset medium:

• Keep 4K: 8.5 seconds, 27.5 MB out.
• Scale to 1080p (-vf scale=1920:-2:flags=lanczos): 3.9 seconds, 3.1 MB out - about nine times smaller and more than twice as fast.

A synthetic pattern compresses differently from camera footage, so treat the ratios as direction, not a promise; the direction holds because a quarter of the pixels is a quarter of the work. The -2 keeps the height even, which H.264 requires, and Lanczos keeps fine detail sharper than the default scaler. In HandBrake, the same move is the resolution limit setting on the Dimensions tab.

Picking in one pass

• Folder of files, interface wanted: HandBrake queue. Terminal is fine: one ffmpeg loop with -n.
• Footage that must stay private: desktop only, or a tool that runs inside the browser tab.
• Old format: ffprobe first. H.264 or MPEG-4 inside - remux. WMV codec - re-encode.
• 4K with a 1080p destination: scale in the same encode.
• Free tier limits in the way: the free converter limits roundup lists every cap with dates.

Once the format is sorted and the next step is cutting a subject out of the footage, the main background removal guide picks up from there.

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