no sound on .mov sent via iMessage

Does anyone know why this may be? I have often sent videos via iMessage to family and friends, and never have a problem with the sound.

Your first step should be to determine if the received file contains an active audio track. If missing or inactive, then you can turn your attention to finding out how the audio track was turned off or deleted from the file when sent . If present and active, then you can look for an audio playback issue between your "work computer" and the audio track of the file—e.g., system audio playback muted/turned down, file audio data, file audio level, etc.

But how do I determine if the received file has an active audio track?

I normally use the QT 7 Pro "Properties" window to check/modify active track settings. MediaInfo, I believe, will show a "Default: No" setting in the info window for the deactivated audio track. (Not sure how Atom Inspector or Dumpster denote deactivated audio tracks but assume both apps can view/modify the status.) However, in most cases an inactive audio track simply does not appear in the QT 7/X "Inspector" window—i.e., the file simply appears to have no audio track even when the data is still stored in the file.

Let me add a couple details: I tried to play the received file on my Mac Pro both with QuickTime and by importing into iTunes, with no sound either way. The sound also does not play from within the Messages App on my Mac Pro.

What do the QT "Inspector" and Finder "Info" windows say about the file? I.e., if the QT "Inspector" window says the file does not contain an audio track but the Finder "Info" window indicates an audio track is present, then the file contains an "inactive" audio track that needs to either be turned on for normal QT app access or used in an app that ignores the Active/Inactive "status" flag.

Excample:

Oops, our messages crossed paths, and I just read your last post. I'll upload the Finder Info window. To be honest I can't tell whether the QT window indicates audio is present, and I don't know how to turn on the audio if it's inactive. Can you tell me how?

Both windows (Finder "Info" Codecs and QT "Inspector" Format lines) indicate the file contains a video (H.264) and audio (AAC) track. I.e., the file looks normal. This implies that either the system is muted/audio turned down too low for audio playback or that the file audio levels were recorded at too low a level for playback. You should check your system playback settings (volume/mute controls), speaker/output selection/settings, etc., and then try playing the file at different volume levels. Other possibilities would be incompatible data rate/sampling combination (not likely since most Apple apps automatically preclude the use of such settings) or a "null" duration and/or data read for the standard 44.1KHz sampling rate indicated (also unlikely since this usually requires processing by a third-party app like that used to create MP4 files from security videos as seen earlier last week in this forum.) Former issues can be checked by you but latter ones normally require examination of the file itself.

So perhaps it's some settings in QT? I don't use QT much, so I'm a little confused, because I don't see a way to access QT Preferences.

Primary QTP X setting is the playback volume control—but that should automatically reset to the default level (0db) embedded in the file each time the file is opened. So unless you reset this in some app to a zero (or near zero) level and saved that setting to the file (simply check the playback volume level in the QT player when it opens in the QT Player app, this is unlikely... and, in which case you need only turn up the volume after the file opens.

Basically, your troubleshooting proves that the file data is in tact and that this is a "playback" issue—either volume setting in the player/file (most likely) or a system setting (unlikely since I assume you changed nothing in the system settings between attempting to play the original MOV file and actually playing the M4A file). Even then, changing the default volume level (e.g., with QT 7 Pro—yes it's "legacy" but still provides many composite/layer/property editing features/settings not accessible in QTPX) is normally ignored by the QT X player. As to app preferences, the QT X player has no accessible user preference panel (but can "automatically" set some settings when performing certain actions while certain system preferences are in effect).

I don't use QT much, so I'm a little confused, because I don't see a way to access QT Preferences.

Again, this seems to imply the problem is in the QTPX itself and the only real volume control is the one displayed in the player when the mouse hovers over the display. You did check it, right?