I want to export a movie with AVAssetWriter
and can't figure out how to include video and audio tracks in sync. Exporting only video works fine, but when I add audio the resulting movie looks like this:
First I see the video (without audio), then the video freezes (showing the last image frame until the end) and after some seconds I hear the audio.
I tried some things with CMSampleBufferSetOutputPresentationTimeStamp
(subtracting the first CMSampleBufferGetPresentationTimeStamp
from the current) for the audio, but it all didn't work and I don't think it is the right direction, since video & audio in the source movie should be in sync anyway...
My setup in short: I create an AVAssetReader
and 2 AVAssetReaderTrackOutput
(one for video, one for audio) and add them to the AVAssetReader
, then I create an AVAssetWriter
and 2 AVAssetWriterInput
(video & audio) and add them to the AVAssetWriter
... I start it all up with:
[assetReader startReading];
[assetWriter startWriting];
[assetWriter startSessionAtSourceTime:kCMTimeZero];
Then I run 2 queues for doing the sample buffer stuff:
dispatch_queue_t queueVideo=dispatch_queue_create("assetVideoWriterQueue", NULL);
[assetWriterVideoInput requestMediaDataWhenReadyOnQueue:queueVideo usingBlock:^
{
while([assetWriterVideoInput isReadyForMoreMediaData])
{
CMSampleBufferRef sampleBuffer=[assetReaderVideoOutput copyNextSampleBuffer];
if(sampleBuffer)
{
[assetWriterVideoInput appendSampleBuffer:sampleBuffer];
CFRelease(sampleBuffer);
} else
{
[assetWriterVideoInput markAsFinished];
dispatch_release(queueVideo);
videoFinished=YES;
break;
}
}
}];
dispatch_queue_t queueAudio=dispatch_queue_create("assetAudioWriterQueue", NULL);
[assetWriterAudioInput requestMediaDataWhenReadyOnQueue:queueAudio usingBlock:^
{
while([assetWriterAudioInput isReadyForMoreMediaData])
{
CMSampleBufferRef sampleBuffer=[assetReaderAudioOutput copyNextSampleBuffer];
if(sampleBuffer)
{
[assetWriterAudioInput appendSampleBuffer:sampleBuffer];
CFRelease(sampleBuffer);
} else
{
[assetWriterAudioInput markAsFinished];
dispatch_release(queueAudio);
audioFinished=YES;
break;
}
}
}];
In the main loop I wait for both queues until they finish:
while(!videoFinished && !audioFinished)
{
sleep(1);
}
[assetWriter finishWriting];
Furthermore I try to save the resulting file in the library with the following code...
NSURL *url=[[NSURL alloc] initFileURLWithPath:path];
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
if([library videoAtPathIsCompatibleWithSavedPhotosAlbum:url])
{
[library writeVideoAtPathToSavedPhotosAlbum:url completionBlock:^(NSURL *assetURL, NSError *error)
{
if(error)
NSLog(@"error=%@",error.localizedDescription);
else
NSLog(@"completed...");
}];
} else
NSLog(@"error, video not saved...");
[library release];
[url release];
...but I get the error:
Video /Users/cb/Library/Application Support/iPhone Simulator/4.2/Applications/E9865BF9-D190-4912-9248-66768B1AB635/Documents/export.mp4 cannot be saved to the saved photos album: Error Domain=NSOSStatusErrorDomain Code=-12950 "Movie could not be played." UserInfo=0x5e4fb90 {NSLocalizedDescription=Movie could not be played.}
The code works without problems in another program. So something is wrong with the movie...?
-(void)mergeAudioVideo
{
NSString *videoOutputPath=[_documentsDirectory stringByAppendingPathComponent:@"dummy_video.mp4"];
NSString *outputFilePath = [_documentsDirectory stringByAppendingPathComponent:@"final_video.mp4"];
if ([[NSFileManager defaultManager]fileExistsAtPath:outputFilePath])
[[NSFileManager defaultManager]removeItemAtPath:outputFilePath error:nil];
NSURL *outputFileUrl = [NSURL fileURLWithPath:outputFilePath];
NSString *filePath = [_documentsDirectory stringByAppendingPathComponent:@"newFile.m4a"];
AVMutableComposition* mixComposition = [AVMutableComposition composition];
NSURL *audio_inputFileUrl = [NSURL fileURLWithPath:filePath];
NSURL *video_inputFileUrl = [NSURL fileURLWithPath:videoOutputPath];
CMTime nextClipStartTime = kCMTimeZero;
AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:video_inputFileUrl options:nil];
CMTimeRange video_timeRange = CMTimeRangeMake(kCMTimeZero,videoAsset.duration);
AVMutableCompositionTrack *a_compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[a_compositionVideoTrack insertTimeRange:video_timeRange ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];
AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:audio_inputFileUrl options:nil];
CMTimeRange audio_timeRange = CMTimeRangeMake(kCMTimeZero, audioAsset.duration);
AVMutableCompositionTrack *b_compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[b_compositionAudioTrack insertTimeRange:audio_timeRange ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:nextClipStartTime error:nil];
AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetMediumQuality];
_assetExport.outputFileType = @"com.apple.quicktime-movie";
_assetExport.outputURL = outputFileUrl;
[_assetExport exportAsynchronouslyWithCompletionHandler:
^(void ) {
if (_assetExport.status == AVAssetExportSessionStatusCompleted) {
//Write Code Here to Continue
}
else {
//Write Fail Code here
}
}
];
}
You can use this code to merge audio and video.
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