How to embed text (caption) a video in iOS in realtime?

Question

I would like to embed a text on a video as it records, then save it in the Camera Roll. When this video is played on any other device this text should show

Answer 1

From here: How can I add overlay text on a video, then re-encode it?

Note this is not updated for ARC, but should give you a good idea about the methodology. This example includes adding images and text, there may be a faster way using iOS 7 APIs/CoreText.

Also: Real time compositing on a video like this would mean decompressing the necessary frames to bitmaps, drawing the text, then recompressing the video. This is an expensive operation and performance may be poor. This is not the kind of thing that lends itself to mobile applications.

Here is the code to add text and image in the Video file.That may help you.

AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:[NSURL fileURLWithPath:videoName]  options:nil];

AVMutableComposition* mixComposition = [AVMutableComposition composition];

AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

AVAssetTrack *clipVideoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) ofTrack:clipVideoTrack atTime:kCMTimeZero error:nil];

[compositionVideoTrack setPreferredTransform:[[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] preferredTransform]];

CGSize videoSize = [clipVideoTrack naturalSize]; 

UIImage *myImage = [UIImage imageNamed:@"29.png"];
CALayer *aLayer = [CALayer layer];
aLayer.contents = (id)myImage.CGImage;
aLayer.frame = CGRectMake(videoSize.width - 65, videoSize.height - 75, 57, 57);
aLayer.opacity = 0.65;
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
videoLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:aLayer];

CATextLayer *titleLayer = [CATextLayer layer];
titleLayer.string = @"Text goes here";
titleLayer.font = @"Helvetica";
titleLayer.fontSize = videoSize.height / 6;
//?? titleLayer.shadowOpacity = 0.5;
titleLayer.alignmentMode = kCAAlignmentCenter;
titleLayer.bounds = CGRectMake(0, 0, videoSize.width, videoSize.height / 6); //You may need to adjust this for proper display
[parentLayer addSublayer:titleLayer]; //ONLY IF WE ADDED TEXT

AVMutableVideoComposition* videoComp = [[AVMutableVideoComposition videoComposition] retain];
videoComp.renderSize = videoSize;
videoComp.frameDuration = CMTimeMake(1, 30);
videoComp.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [mixComposition duration]);
AVAssetTrack *videoTrack = [[mixComposition tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction];
videoComp.instructions = [NSArray arrayWithObject: instruction];

AVAssetExportSession *assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];//AVAssetExportPresetPassthrough
assetExport.videoComposition = videoComp;

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString* VideoName = [NSString stringWithFormat:@"%@/mynewwatermarkedvideo.mp4",documentsDirectory];


 //NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:VideoName];
NSURL *exportUrl = [NSURL fileURLWithPath:VideoName];

if ([[NSFileManager defaultManager] fileExistsAtPath:VideoName])
{
    [[NSFileManager defaultManager] removeItemAtPath:VideoName error:nil];
}

assetExport.outputFileType = AVFileTypeQuickTimeMovie;
assetExport.outputURL = exportUrl;
assetExport.shouldOptimizeForNetworkUse = YES;

 //[strRecordedFilename setString: exportPath];

[assetExport exportAsynchronouslyWithCompletionHandler:
 ^(void ) {
     [assetExport release];
     dispatch_async(dispatch_get_main_queue(), ^{
         [self exportDidFinish:assetExport];
     });
 }
 ];

[videoAsset release];

}

 -(void)exportDidFinish:(AVAssetExportSession*)session
{
    NSURL *exportUrl = session.outputURL;
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];

    if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:exportUrl])
    {
        [library writeVideoAtPathToSavedPhotosAlbum:exportUrl completionBlock:^(NSURL *assetURL, NSError *error)
        {
            dispatch_async(dispatch_get_main_queue(), ^{
                if (error) {
                    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Video Saving Failed"
                                                                   delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
                    [alert show];
                } else {
                    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Video Saved" message:@"Saved To Photo Album"
                                                                   delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
                    [alert show];
                }
            });
        }];

    }
    NSLog(@"Completed");
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"AlertView" message:@"Video is edited successfully." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
    [alert release];

}