ffmpeg can produce pseudo-corrupt audio when ‘copy’ing to an MP4 container

I’ve been using ffmpeg to trim clips from a trail camera, as most of the time there’s only a few seconds of anything interesting in frame out of the 30+ seconds of video it records each time, but I don’t want to re-encode them and lose video quality as a result (or balloon file sizes tremendously with a lossless video coding).  Keeping the whole 30 seconds is not just unnecessary and makes viewing the videos much more tedious, but wasteful of storage space as the encoding quality from the trail camera is very inefficient (file sizes are many times larger than they should be for the quality – clearly the H.264 encoder used in the trail camera is very cheap and very bad at its job).

I was originally doing something like:

ffmpeg -ss 00:07 -t 00:03 -i "IMG_0164.MP4" -async 1 -c copy "IMG_0164_TRIMMED.MP4"

The resulting trimmed MP4s play just fine in Quicktime, the Finder – anywhere that uses Apple’s decoding libraries (though I didn’t test iOS).

However, in VLC, or Lightroom, the audio is completely corrupt – just incoherent noise.  In Lightroom the video doesn’t even play correctly, because of Lightroom’s stupid habit of re-encoding the video & audio into internal caches – apparently their video decoder is somehow thrown off by the audio channel issues, too.

After much trial and error and many dead-ends (thank you completely bogus & wrong Stack Overflow threads… sigh) I eventually realised that the problem is apparently simply that Lightroom, VLC, etc get offended when you include pcm_s16le audio in an MP4.  ffmpeg itself says that’s not a valid audio codec for the MP4 container, iff you explicitly tell it to use that as the codec.  If you’re just copying from an existing audio / video file, however, it makes no mention at all of the concern.  Sigh.

So the apparent solution is simply to switch to the MOV container format instead.

ffmpeg -ss 00:07 -t 00:03 -i "IMG_0164.MP4" -async 1 -c copy "IMG_0164_TRIMMED.MOV"

The encoded bits remain identical, but the MOV container apparently accepts PCM audio where MP4 does not.  VLC, Lightroom, etc are now happy (and Quicktime et al remain happy).

(another possibility is that the ‘incompatibility’ is related to MP4 levels or some other such junk… I didn’t try deciphering or exploring that)

It’s frustrating that VLC & Lightroom can’t handle this when clearly it’s technically possible (witness Quicktime), and worse they don’t even properly recognise that they’re not handling it properly – they just play completely corrupt audio that’s literally painful on the ears.

It’s also very curious that the trail camera uses PCM audio if that’s not valid in an MP4 container.  It’s downright bizarre that VLC & Lightroom can play the unmodified MP4s straight from the trail camera, even though they use the same purportedly invalid audio codec… somehow something ffmpeg is doing during its transmutation is making them angry.  I was unable to determine what that might be, though, through trial-and-error with ffmpeg command line options & rudimentary examination of the input & output files.

P.S.  An alternative is to bitwise-copy only the video stream (i.e. change -c copy to -c:v copy), and let VLC transcode the audio into its default AAC for the MP4 container.  That probably wouldn’t be a problem for me in my case – the audio from trail cameras is pretty crappy to begin with – but at the same time the audio tracks in these files are insignificant in size, so re-encoding them (and lossy as AAC) is pointless to saving disk space.

Apple Mail crashes on launch if connection logging is enabled

This was a fun one.  Mail started crashing on launch for absolutely no apparent reason – nothing had changed to its config or similar in a long time.  The crash logs were all fingering an identical culprit – -[IMAPTaskManager secondaryIdleMailboxName] called on the wrong GCD queue:

Process: Mail [19884]
Path: /Applications/Mail.app/Contents/MacOS/Mail
Identifier: com.apple.mail
Version: 11.3 (3445.6.18)
Build Info: Mail-3445006018000000~4
Code Type: X86-64 (Native)
Parent Process: ??? [1]
Responsible: Mail [19884]
User ID: …

Date/Time: 2018-04-19 16:44:45.717 -0700
OS Version: Mac OS X 10.13.4 (17E199)
Report Version: 12
Anonymous UUID: …

Sleep/Wake UUID: …

Time Awake Since Boot: 94000 seconds
Time Since Wake: 530 seconds

System Integrity Protection: enabled

Crashed Thread: 13 Dispatch queue: Task Manager Serialization Queue (QOS: UNSPECIFIED)

Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY

Application Specific Information:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'This method should only be called on the serialization queue'
terminating with uncaught exception of type NSException
abort() called

Application Specific Backtrace 1:
0 CoreFoundation 0x00007fff55da96bb __exceptionPreprocess + 171
1 libobjc.A.dylib 0x00007fff7d4c1942 objc_exception_throw + 48
2 CoreFoundation 0x00007fff55daf2a2 +[NSException raise:format:arguments:] + 98
3 Foundation 0x00007fff57ee7340 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 193
4 IMAP 0x00007fff6fe88959 -[IMAPTaskManager secondaryIdleMailboxName] + 216
5 IMAP 0x00007fff6fe880cb -[IMAPTask mailboxIsUserVisibleUsingDataSource:] + 180
6 IMAP 0x00007fff6fe6ab68 -[IMAPMailboxSyncTask _nextNetworkPriorityAndOperation:reservedNetworkPriority:] + 164
7 IMAP 0x00007fff6fe6c4ba -[IMAPMailboxSyncTask recalculatePriorities] + 398
8 IMAP 0x00007fff6fe67dd9 -[IMAPMailboxSyncTask initWithDataSource:taskManager:imapMailbox:fromStatus:forceFullSync:] + 766
9 IMAP 0x00007fff6fe931f7 -[IMAPTaskManager _syncMailboxWithDataSource:withIMAPMailbox:fromStatus:forceFullSync:userInitiated:] + 370
10 IMAP 0x00007fff6fe92e68 -[IMAPTaskManager syncMailboxWithDataSource:withIMAPMailbox:fromStatus:forceFullSync:userInitiated:] + 240
11 IMAP 0x00007fff6fe9631a -[IMAPTaskManager didAddMessagesWithUnknownUID:toDataSource:] + 872
12 Foundation 0x00007fff57e4a5df __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 7
13 Foundation 0x00007fff57e4a441 -[NSBlockOperation main] + 68
14 Foundation 0x00007fff57e488ee -[__NSOperationInternal _start:] + 778
15 Foundation 0x00007fff57e44917 __NSOQSchedule_f + 369
16 libdispatch.dylib 0x00007fff7e09ee08 _dispatch_client_callout + 8
17 libdispatch.dylib 0x00007fff7e0b1ed1 _dispatch_continuation_pop + 472
18 libdispatch.dylib 0x00007fff7e0a9783 _dispatch_async_redirect_invoke + 703
19 libdispatch.dylib 0x00007fff7e0a09f9 _dispatch_root_queue_drain + 515
20 libdispatch.dylib 0x00007fff7e0a07a5 _dispatch_worker_thread3 + 101
21 libsystem_pthread.dylib 0x00007fff7e3f0169 _pthread_wqthread + 1387
22 libsystem_pthread.dylib 0x00007fff7e3efbe9 start_wqthread + 13

Long story short, the issue turns out to be having connection logging enabled.  That’d been turned on many months before in order to debug a different stupid Mail bug, and had been simply left on (deliberately IIRC, since Mail tends to bug-out quite often, so why not have logs already available when it comes time to debug it yet again?).

Connection logging is enabled or disabled by opening the “Connection Doctor” (Window menu > Connection Doctor) and using the checkbox titled “Log Connection Activity”.

So how do you get to that checkbox when Mail crashes on launch?  Well, in this specific instance I was able to disable all mail accounts via System Preference’s Accounts pane, launch Mail, disable logging, quit Mail, re-enable all mail accounts via System Preferences, and then relaunch Mail to have it finally actually work.

From even just brief web searching, it’s clear that this issue has been present and well-known in Mail for a really long time.  Sigh.  Apple’s protestations that they care about software quality, or the Mac, are relentlessly undermined by their actual actions.

‘Fake error’ about immutable values when using popFirst() on Array

It’s been a while since I wrote any meaningful Swift.  How I didn’t miss the Swift compiler’s bullshit error messages.

var someArray = ["Foo", "Bar"]

if let foo = someArray.popFirst() {
    print("Who cares, we never get here anyway.")
}

That yields, on the popFirst() method:  “Cannot use mutating member on immutable value: ‘someArray’ is immutable”.

No it’s not.  It’s simply not.

For whatever reason, if you instead call popFirst() on ArraySlice – ostensibly indistinguishable from a real Array – it works just fine.

var someArray = ["Foo", "Bar"][0...]

if let foo = someArray.popFirst() {
    print("Yet this works correctly.")
}

Sigh.

I presume it’s trying to tell me something stupidly obscure about Swift’s byzantine type system.  Good luck finding out what.  Good luck even finding the definition of the popFirst() method, since Xcode claims it doesn’t exist if you Command-Control-click on it.  But Xcode can’t find most things, so that in itself says very little.