MP4 to FLAC

No. MP4 soundtracks are normally AAC, and AAC throws away detail when the video is encoded. FLAC preserves what remains, bit for bit, but it cannot bring back what was thrown away.

FLAC for storage and listening: the same audio at about half the size, with proper tags. WAV when a DAW or an older device will not import FLAC.

Between 50 and 60 percent of the WAV equivalent, so roughly 5 to 6 MB per minute of stereo. Speech and sparse arrangements compress further than dense mixes.

Yes. The Files app has played FLAC since iOS 11, and VLC handled it long before that. Apple Music will not import FLAC, so choose M4A if the file has to go into that library.

Yes. MOV, MKV, AVI, WebM and FLV all go through the same converter with FLAC as the output.

One gigabyte per file. Trim anything larger before converting and send only the part you need.

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