ios - 使用 maxRecordedFileSize 限制 AVCaptureSession 记录时间

Question

我一直在为 iOS 8 编写相机应用程序，它使用 AVFoundation 来设置和处理记录和保存(而不是 ImagePickerController)。我试图保存使用 AVCaptureMovieFileOutput 类的 maxRecordedFileSize 属性，以允许用户填满手机上的所有可用空间(减去 250MB 的缓冲区留给苹果的东西)。

- (unsigned long long) availableFreespaceInMb {
unsigned long long freeSpace;
NSError *error = nil;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSDictionary *dictionary = [[NSFileManager defaultManager] attributesOfFileSystemForPath:[paths lastObject] error: &error];

if (dictionary) {
    NSNumber *fileSystemFreeSizeInBytes = [dictionary objectForKey: NSFileSystemFreeSize];
    freeSpace = [fileSystemFreeSizeInBytes unsignedLongLongValue];

} else {
    NSLog(@"Error getting free space");
    //Handle error
}

//convert to MB
freeSpace = (freeSpace/1024ll)/1024ll;
freeSpace -= _recordSpaceBufferInMb; // 250 MB
NSLog(@"Remaining space in MB: %llu", freeSpace);
NSLog(@"    Diff Since Last: %llu", (_prevRemSpaceMb - freeSpace));

_prevRemSpaceMb = freeSpace;
return freeSpace;

AVErrorMaximumFileSizeReached 当可用空间(减去缓冲区)减少到零时抛出，并且没有抛出保存错误，但视频没有出现在相机胶卷中，也没有被保存。当我设置 maxRecordedDuration 字段时，会抛出 AVErrorMaximumDurationReached 并且视频会保存。我根据最大大小计算最大时间，但由于帧压缩，我总是有足够的空间。

- (void) toggleMovieRecording
{
double factor = 1.0;
if (_currentFramerate == _slowFPS) {
    factor = _slowMotionFactor;
}

double availableRecordTimeInSeconds = [self remainingRecordTimeInSeconds] / factor;
unsigned long long remainingSpace = [self availableFreespaceInMb] * 1024 * 1024;

if (![[self movieFileOutput] isRecording]) {
    if (availableSpaceInMb < 50) {
        NSLog(@"TMR:Not enough space, can't record");
        [AVViewController currentVideoOrientation];
        [_previewView memoryAlert];
        return;
    }
}

if (![self enableRecording]) {
    return;
}

[[self recordButton] setEnabled:NO];

dispatch_async([self sessionQueue], ^{
    if (![[self movieFileOutput] isRecording])
    {            
        if ([[UIDevice currentDevice] isMultitaskingSupported])
        {
            [self setBackgroundRecordingID:[[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil]];
        }

        // Update the orientation on the movie file output video connection before starting recording.
        [[[self movieFileOutput] connectionWithMediaType:AVMediaTypeVideo] setVideoOrientation: [AVViewController currentVideoOrientation]];//[[(AVCaptureVideoPreviewLayer *)[[self previewView] layer] connection] videoOrientation]];

        // Start recording to a temporary file.
        NSString *outputFilePath = [NSTemporaryDirectory() stringByAppendingPathComponent:[@"movie" stringByAppendingPathExtension:@"mov"]];

        // Is there already a file like this?
        NSFileManager *fileManager = [NSFileManager defaultManager];

        if ([fileManager fileExistsAtPath:outputFilePath]) {
            NSLog(@"filexists");
            NSError *err;
            if ([fileManager removeItemAtPath:outputFilePath error:&err] == NO) {
                NSLog(@"Error, file exists at path");
            }
        } 

        [_previewView startRecording];

        // Set the movie file output to stop recording a bit before the phone is full
        [_movieFileOutput setMaxRecordedFileSize:remainingSpace]; // Less than the total remaining space
       // [_movieFileOutput setMaxRecordedDuration:CMTimeMake(availableRecordTimeInSeconds, 1.0)];

        [_movieFileOutput startRecordingToOutputFileURL:[NSURL fileURLWithPath:outputFilePath] recordingDelegate:self];
    }
    else
    {
        [_previewView stopRecording];
        [[self movieFileOutput] stopRecording];
    }
});
}

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error

NSLog(@"AVViewController: didFinishRecordingToOutputFile");

if (error) {
    NSLog(@"%@", error);
    NSLog(@"Caught Error");
    if ([error code] == AVErrorDiskFull) {
        NSLog(@"Caught disk full error");
    } else if ([error code] == AVErrorMaximumFileSizeReached) {
        NSLog(@"Caught max file size error");
    } else if ([error code] == AVErrorMaximumDurationReached) {
        NSLog(@"Caught max duration error");
    } else {
        NSLog(@"Caught other error");
    }

    [self remainingRecordTimeInSeconds];

    dispatch_async(dispatch_get_main_queue(), ^{
        [_previewView stopRecording];
        [_previewView memoryAlert];
    });
}

// Note the backgroundRecordingID for use in the ALAssetsLibrary completion handler to end the background task associated with this recording. This allows a new recording to be started, associated with a new UIBackgroundTaskIdentifier, once the movie file output's -isRecording is back to NO — which happens sometime after this method returns.
UIBackgroundTaskIdentifier backgroundRecordingID = [self backgroundRecordingID];
[self setBackgroundRecordingID:UIBackgroundTaskInvalid];

[[[ALAssetsLibrary alloc] init] writeVideoAtPathToSavedPhotosAlbum:outputFileURL completionBlock:^(NSURL *assetURL, NSError *error) {
    if (error) {
        NSLog(@"%@", error);
        NSLog(@"Error during write");
    } else {
        NSLog(@"Writing to photos album");
    }

    [[NSFileManager defaultManager] removeItemAtURL:outputFileURL error:nil];

    if (backgroundRecordingID != UIBackgroundTaskInvalid)
        [[UIApplication sharedApplication] endBackgroundTask:backgroundRecordingID];
}];

if (error) {
    [_session stopRunning];
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC), _sessionQueue, ^{
        [_session startRunning];
    });
}

当两个错误都被抛出时，会出现“正在写入相册”。我完全被这个难住了。任何 iOS 见解？

Answer 1

您提供的代码示例很难测试，因为缺少属性和方法。虽然我无法编译您的代码，但肯定有一些危险信号可能会导致问题。在内部发现了以下问题: captureOutput:didFinishRecordingToOutputFileAtURL:fromConnections:error:

问题 1:该方法正在处理传入的错误，但随后继续执行该方法。相反，它应该是:

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error { 
    if (error) {
        // handle error then bail
        return;
    }

    // continue on
}

问题 2:您正在实例化的 ALAssetsLibrary 对象未存储到属性中，因此一旦 captureOutput:didFinishRecordingToOutputFileAtURL:fromConnections:error: 完成该对象将被释放(可能永远不会触发您的完成堵塞)。相反，它应该是:

// hold onto the assets library beyond this scope
self.assetsLibrary = [[ALAssetsLibrary alloc] init];

// get weak reference to self for later removal of the assets library
__weak typeof(self) weakSelf = self;
[self.assetsLibrary writeVideoAtPathToSavedPhotosAlbum:outputFileURL completionBlock:^(NSURL *assetURL, NSError *error) {
    // handle error
    // handle cleanup

    // cleanup new property
    weakSelf.assetsLibrary = nil;
}];

如果解决这些问题不能解决问题，请提供缺少的代码以使您的示例编译。