Nowadays most people use Netflix or similar streaming services for watching movies, but many old hands have sizeable older movie collections, brilliant classics you won't find streamed anywhere. No matter how you have amassed the movies, whether from old DVDs or downloaded, chances are you have several copies of many of those classic movies. If you think that the average movie has a file size over 1GB, you don't need many of those duplicates to choke up your hard disks. To tidy up your collection, save space and keep the best quality version of each movie, you need a duplicate detector tool, but how do you pick one? There are 102 alternatives to i-DeClone for Windows 7/10/11, both free and paid. This review will help you choose the best duplicate movie cleaner software.

How do you discover near-duplicate video?

Recognizing movies calls for specialized software that can decompress and extract the video and audio streams from the movie file, then use a number of algorithms to compare them and discover similar movies. Some programs compare a succession of thumbnails (frames) using similar image detection methods, others focus on the soundtrack and use audio fingerprints to align and compare the audio streams. Such visual or audio algorithms can be used to compare movies, and see through differences in video resolutions, frame rates and dimensions, soundtrack loudness etc, to identify visually identical files — as opposed to binary-identical.

Some simpler duplicate files software ignore the audio/video content and try to find similar movies using file attributes like the name and duration. This is next to impossible for movies, where there is no universally accepted tagging system (like ID3 tags for MP3 music). Take for instance the following 2 video files. It is the same movie, but the file sizes and durations vary slightly, one is widescreen HD and the other 720p — still they represent the same movie!

What we need therefore is software that can find movie content duplicates, allowing for differences in HD resolution and file formats (WMV,AVI,MOV,ASX,MKV,MP4,ASF,MTS,TTS...). Media files need a computer program that can understand the video, not the raw bytes stored in them. The bytes may differ, even the picture quality itself slightly, but video-aware software will detect the similarity, almost as a human movie watcher would.

Most of the aforementioned 102 duplicate cleaners are not "movie savvy". I have narrowed it down to just six (6) computer programs (for Windows 7/10/11) that analyze the movies for similarity and will find video duplicates, which in alphabetical order are:

• Czkawka by Rafał Mikrut [CZK]
• Duplicate Media Finder [DMF]
• Duplicate video search by Bolide software [DVS]
• i-DeClone by Zabkat [IDE]
• Video comparer by Eric Bohain [VCO]
• Video duplicate finder (open source, various contributors) [VDF]

I will also consider another popular program called Auslogics duplicate file finder, just to show you how "naive" duplicate finders are not up to the task of discovering duplicate movies. Some of these programs are free or open source, and some shareware with free trial, so you would expect a decent quality in departments such as:

• Handle many video file types, not just AVI
• Easy to use for Average Joe consumer
• Affordable, preferably without annual subscriptions
• Discover many near-duplicates with the least effort (fast)
• Make few mistakes (false positives)
• Handle lots of files without bugs and crashes (robust)

Before we begin the Video Clone Olympics, here's a table summarizing the main contenders for the title of Best duplicate video detective Windows software. Some are specialized for similar movies, others can handle also similar music and images. 64-bit programs are capable of handling huge media collections (32-bit programs are limited to 2GB memory)

Name/Website Version   Price   (US $) Download   size (MB) 64 bit   Audio   Video   Images Notes     ■ Czkawka [CZK] 5.02 — 45.6 open source requires ffmpeg   ■ Duplicate Media Finder [DMF] 9.01 $46 26.6 —     ■ Duplicate video search [DVS] 2.3 $30 15.5 — — — separate programs sold for music etc   ■ i-DeClone [IDE] 1.54 $30 2.3     ■ Video comparer [VCO] 1.07 $30 14.3 — —   ■ Video duplicate finder [VDF] 1.0 (?) — 65.7 — open source cross platform   ■ Auslogics duplicate file finder [AUD] 10.0 — 16.7 — scans bytes, not video

Typical workflow for finding and removing duplicate files

The workflow of all duplicate file removers more or less comprises 5 basic steps:

1. Choose where to search. Define the search scope in certain folders or your entire PC and attached hard disks and other devices like phones.
2. Choose what and how to search. We are searching for movie files; there are many search options that affect the speed and quality of the results. For this review we concentrate on similar video content, and the most important parameter is the similarity tolerance, a percent that shows how much similar 2 movie files should be to be considered duplicate. Lowering the similarity threshold will catch more duplicate movies but will also produce false positives, films that are completely different.
3. Wait for results and preview. Audio/Video fingerprint scanning is slow by nature, but you don't need to sit on top of the duplicate scanner while it is searching. Once the results are in, you examine them to make sure the duplicate groups are correct. If you find any mistakes (false positives) in the results, you can remove the wrong files from further processing.
4. Choose what to keep and what to remove. Once the search is finished, duplicate files are grouped together and offer a way to choose what is kept and what gets deleted. Mostly this is done using checkboxes. Manual selection is impractical when many duplicates are found, so programs offer various automatic ways to choose what gets deleted, e.g. the lowest resolution films, or the smallest file sizes (poor picture quality)
5. Clean up marked items. Finally we want to remove duplicates and free up the hard disk space. This is either done by deleting the duplicate files, or replacing them with hard/symbolic links, which are like file shortcuts that don't take up much space. Some programs allow moving the duplicates in a separate folder, although I don't see the point — other than perhaps as a temporary measure. The goal is freeing up disk space and reducing junk and clutter from our movie collection.
   

    

   We are talking about similar movies, but what we are really after is identical films. We are not trying to find Star Wars episode IV similar to episode V, we want to see if we have Star Wars episode IV more than once in our collection. "Similarity" enters the picture because no 2 movie files are byte-identical, on account of resolution, quality and such parameters.