Convert DivX to MP3 - extract audio
DivX files are almost always AVI containers with MPEG-4 Part 2 video and MP3 audio. When the audio is already MP3, Wave copies the samples straight through - no decoding, no re-encoding (a straight extract; see Remux vs re-encode). AC-3 and MP2 tracks re-encode cleanly through LAME.
What actually changes
A DivX file is an AVI container with MPEG-4 Part 2 ASP video and, in the overwhelming majority of cases, an MP3 audio track. Wave inspects the audio and takes the fast path when it can: MP3-in-AVI is a bit-exact stream copy - the bytes that were the audio track in the AVI become the bytes of the MP3 file, without a single sample being decoded. The extract finishes in seconds even for a two-hour DVD rip, and the output MP3 has exactly the same bitrate, sample rate, and stereo image as the source.
When a DivX file carries AC-3 (some Xvid rips of AC-3-mastered DVDs, or hardware-encoded DivX with 5.1 audio) or MP2 (rare, mostly early European DivX), Wave decodes the audio in your browser and re-encodes to MP3 through libmp3lame at 192 kbps. AC-3 5.1 tracks downmix to stereo respecting the Dolby downmix metadata in the source, so the dialogue stays centred and the effects hold their approximate position. Video is discarded entirely, so the extract is much faster than any full-file re-encode.
The reason MP3 dominates DivX audio is historical. DivX rose alongside the DVD-rip scene of the early 2000s, and the DivX-Certified DVD players that appeared in 2004 (Philips DVP-642 being the archetype) required MP3 or AC-3 audio for compatibility. Rippers standardised on MP3 because it was the same format their music library already used, and the AVI-with-MP3 combination became the dominant DivX pairing for over a decade. Xvid files - the open-source fork of DivX - follow the same audio convention, and Wave treats them identically.
Typical DivX MP3 audio bitrates cluster at 128 kbps (space-conscious rips), 160 kbps (Xvid default), and 192 kbps (higher-quality rips). Because Wave copies the stream through without touching a sample, the MP3 file preserves whichever bitrate the source encoder chose. If your DivX rip has a 320 kbps MP3 audio track (music-focused encodes sometimes did this), you get a 320 kbps MP3. Nothing is normalised, nothing is re-quantised.
Three steps.
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Step 1
Drop the .divx, .avi, or .div file onto the card.
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Step 2
Pick MP3 as the output format on the inspect screen.
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Step 3
Convert. Save the MP3.
Answers, specifically.
Is the extract really lossless if the source is MP3?
Yes. Wave detects MP3-in-AVI during inspect and takes a copy path - the audio samples are moved from the AVI into a standalone MP3 file without ever being decoded. Bit-exact. You can confirm with a hex diff of the audio payloads.
What about 5.1 AC-3 audio in some Xvid rips?
AC-3 decodes to stereo through the Dolby downmix coefficients in the stream, then re-encodes to MP3 at 192 kbps. The dialogue stays anchored to the centre and effects preserve their left/right placement.
Is Xvid handled the same way as DivX?
Yes. Xvid is the open-source MPEG-4 Part 2 codec; the audio pairing conventions are identical. Wave treats DivX and Xvid AVIs the same for the audio-extract path.
Does the .div extension work too?
Yes. .div, .divx, and .avi are all treated identically - the file header decides the container, not the extension.
My rip has commentary on a second audio track. Which one gets extracted?
The default-flagged track. AVI has weak conventions for marking default audio, so the first audio stream in the file is Wave's pick when no default flag exists. Multi-track extraction is on the roadmap.
Will the MP3 have ID3 tags?
A basic title tag is written from the AVI's optional INFO chunk if the source has one. Most DivX rips do not carry per-track metadata, so the MP3 usually arrives untagged - name it after the movie or run it through any tag editor.
DivX 3D or DivX Plus HD?
DivX Plus HD (H.264 in Matroska) is not a DivX file for Wave's purposes - use MKV to MP3 for that. DivX 3D uses stereoscopic MPEG-4 Part 2 in AVI; audio is standard MP3 and extracts through the same path as any other DivX file.
What about the audio in DivX-encoded home movies from camcorders?
Consumer camcorder DivX (some Toshiba and JVC hard-disc camcorders from the mid-2000s) usually paired MPEG-4 Part 2 with MP3 or AC-3 at 128 kbps stereo. Both paths work in Wave - MP3 sources copy through, AC-3 re-encodes.