我正在制作一个向视频添加主题音乐的应用程序。
有些用户抱怨如果他们的音乐是苹果无损格式,视频会太大。
我发现这是因为AVMutableComposition
我使用的只是将原始音乐格式放入我生成的视频中。
那么有什么办法可以降低 MPMediaItem 中音乐的比特率,或者改变它的编码格式?
这是我用来向视频添加音乐的代码片段。
AVMutableComposition* mixComposition = [AVMutableComposition composition];
AVMutableCompositionTrack *compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio
preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]
atTime:kCMTimeZero error:nil];
AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
atTime:kCMTimeZero error:nil];
AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition
presetName:AVAssetExportPresetPassthrough];
NSURL *exportUrl = [NSURL fileURLWithPath:_videoOutputPath];
if ([[NSFileManager defaultManager] fileExistsAtPath:_videoOutputPath]){
[[NSFileManager defaultManager] removeItemAtPath:_videoOutputPath error:nil];
}
_assetExport.outputFileType = @"com.apple.quicktime-movie";
_assetExport.outputURL = exportUrl;
_assetExport.shouldOptimizeForNetworkUse = YES;
[_assetExport exportAsynchronouslyWithCompletionHandler:^(void ) {}