Video codec and audio codec answer different questions
MOV is the QuickTime movie container. It can hold separate picture and sound tracks with their own codecs. An iPhone Camera recording commonly uses H.264 or HEVC for the picture and AAC for sound, but AAC is not guaranteed in every MOV made by a camera or editor.
PrivateMP3 does not decode H.264 or HEVC frames when making an audio file. Once the MOV structure is open, it selects an audio track and ignores the pictures. That means extraction can work even when the browser cannot preview the video. It does not mean every HEVC MOV will work: damaged container metadata or an unsupported audio codec can still stop the job.
AAC decides whether M4A can be copied
MP3 is always a new 192 kbps encode. If the selected MOV track is AAC, M4A can copy its encoded packets only when the complete track is kept with no volume changes. The copy note appears when those conditions are met. A cut, volume edit or non-AAC source makes M4A a new AAC encode. WAV decodes the selected track to 16-bit PCM.
This distinction matters with camera files that use PCM, ALAC or another audio codec. The video may be perfectly ordinary while the M4A copy path is unavailable. Check the audio track, not the H.264 or HEVC label, when deciding which output preserves the source.
The iPhone file picker can be the slow part
Choosing a video from Photos may make iOS prepare or convert a browser-compatible copy before the file input returns. PrivateMP3 has not received the file yet, so it cannot show progress for that wait. Retrieving an original from cloud storage adds another possible delay.
If the video already exists in Files, choose Browse and select it there. That avoids the Photos export step, although a cloud-only Files item still has to download. Once the filename appears on this page, the hand-off is complete and PrivateMP3 starts scanning the local file.
If the MOV has pictures but no usable audio
Play the original and confirm that it contains sound. If several audio tracks exist, choose the intended language or mix from the track picker. A recording interrupted before it was finalized may lack the metadata needed to locate its tracks. If the container opens but the waveform does not appear, the browser may lack a decoder for the audio codec. A current desktop browser is a useful second check because it removes the iPhone Photos hand-off from the test.