AVI to MP4

Both are containers rather than codecs. AVI normally wraps DivX or Xvid, while MP4 wraps H.264 or HEVC. H.264 is the newer and more efficient compression, which is why the MP4 is smaller at the same quality and why every modern device has a decoder for it built in.

The video is re-encoded, so strictly speaking something is lost. H.264 is efficient enough that at a normal bitrate you cannot tell the MP4 from the AVI, and the file is much smaller.

The audio track uses a codec your player does not have, often AC-3 or MP2. Converting to MP4 re-encodes that track as AAC, and the sound plays.

Keep the resolution and frame rate as they are and set a high bitrate. The MP4 then looks the same as the AVI unless you compare the two frame by frame.

Yes. iOS has never played AVI without a third-party player, which is the most common reason people convert the format. The MP4 opens in Photos, Files and iMessage.

Yes. This AVI to MP4 converter also takes MOV, MKV, WebM, FLV and WMV.

One gigabyte per file. A two-hour standard-definition AVI usually fits. Trim a longer or higher-resolution source before you convert it.

Uploads travel over HTTPS. The source file and the finished MP4 are both deleted from our servers within minutes of the conversion, and neither is shared with anyone.