Convert DivX to MP4
DivX video is MPEG-4 Part 2 ASP - a codec MP4 accepts directly. Wave usually copies the video and audio into MP4 without touching a single frame, so the conversion is fast and the quality is identical to the source.
What actually changes
DivX started as a hacked build of Microsoft's MPEG-4 Part 2 encoder in 1999, went legitimate around 2001, and became the default codec for DVD rips through the 2000s. Under the FourCC labels DIV3, DIVX, DX50, and the near-identical Xvid (XVID), the actual bitstream is standard MPEG-4 Part 2 ASP. MP4 was defined to hold exactly this codec.
That means a .divx file (or a .avi containing DivX video) can usually go straight into MP4 by rewriting the container header - no decoding, no re-encoding, no quality loss. Audio is nearly always MP3, which MP4 also accepts as-is. Wave inspects the source, confirms the codecs, and performs a fast re-mux. When Wave finds unusual audio (AC-3 5.1, some old MP2 streams), only the audio re-encodes; the video still copies.
Three steps.
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Step 1
Drop the .divx or .avi file onto the card.
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Step 2
Wave inspects and shows Fast copy - DivX video and MP3 audio are already MP4-compatible.
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Step 3
Convert and save the MP4.
Answers, specifically.
Isn't DivX outdated?
For new encodes, yes - H.264 and HEVC beat MPEG-4 Part 2 on efficiency. But DivX files that already exist play just fine, and re-encoding them to H.264 would lose quality for no visible gain. A pure remux is the right move.
What's the difference between DivX and Xvid?
Codec bitstream: nothing meaningful - both are MPEG-4 Part 2 ASP. History: DivX was commercial (DivX, Inc.), Xvid was the open-source fork of an early DivX build. Files use different FourCCs (DIVX / DX50 vs XVID) but MP4's mpeg4 codec accepts both.
My iPhone still refuses the MP4. Why?
iOS Safari plays H.264 and HEVC natively but not MPEG-4 Part 2. Some iOS video players match on codec (not extension) and reject a .mp4 containing DivX. On desktop, VLC handles it without complaint; on iOS, the practical fix is a full H.264 re-encode via a converter that offers it.
What about the .div extension?
Same container. Some encoders wrote .div, others .divx, others plain .avi. Wave treats all three the same - the header bytes decide the container, not the extension.
Is DRM-protected DivX supported?
No. A small share of DivX files (mostly circa-2005 online rental content) carry DivX DRM. Wave can't decrypt them, and no browser-side tool can.