使用 AVAssetWriter 进行视频编码 - 崩溃 [英] Video Encoding using AVAssetWriter - CRASHES
问题描述
我有一个功能，可以在 iphone/ipad 上将视频重新编码为可管理的比特率.这是:*更新的工作代码，现在有音频！:) *
I have a function that is supposed to re-encode a video to a manageable bitrate on iphone/ipad. Here it is: *UPDATED WORKING CODE, NOW WITH AUDIO! :) *
-(void)resizeVideo:(NSString*)pathy{
NSString *newName = [pathy stringByAppendingString:@".down.mov"];
NSURL *fullPath = [NSURL fileURLWithPath:newName];
NSURL *path = [NSURL fileURLWithPath:pathy];
NSLog(@"Write Started");
NSError *error = nil;
AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:fullPath fileType:AVFileTypeQuickTimeMovie error:&error];
NSParameterAssert(videoWriter);
AVAsset *avAsset = [[[AVURLAsset alloc] initWithURL:path options:nil] autorelease];
NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoCodecH264, AVVideoCodecKey,
[NSNumber numberWithInt:1280], AVVideoWidthKey,
[NSNumber numberWithInt:720], AVVideoHeightKey,
nil];
AVAssetWriterInput* videoWriterInput = [[AVAssetWriterInput
assetWriterInputWithMediaType:AVMediaTypeVideo
outputSettings:videoSettings] retain];
NSParameterAssert(videoWriterInput);
NSParameterAssert([videoWriter canAddInput:videoWriterInput]);
videoWriterInput.expectsMediaDataInRealTime = YES;
[videoWriter addInput:videoWriterInput];
NSError *aerror = nil;
AVAssetReader *reader = [[AVAssetReader alloc] initWithAsset:avAsset error:&aerror];
AVAssetTrack *videoTrack = [[avAsset tracksWithMediaType:AVMediaTypeVideo]objectAtIndex:0];
videoWriterInput.transform = videoTrack.preferredTransform;
NSDictionary *videoOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
AVAssetReaderTrackOutput *asset_reader_output = [[AVAssetReaderTrackOutput alloc] initWithTrack:videoTrack outputSettings:videoOptions];
[reader addOutput:asset_reader_output];
//audio setup
AVAssetWriterInput* audioWriterInput = [[AVAssetWriterInput
assetWriterInputWithMediaType:AVMediaTypeAudio
outputSettings:nil] retain];
AVAssetReader *audioReader = [[AVAssetReader assetReaderWithAsset:avAsset error:&error] retain];
AVAssetTrack* audioTrack = [[avAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
AVAssetReaderOutput *readerOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:audioTrack outputSettings:nil];
[audioReader addOutput:readerOutput];
NSParameterAssert(audioWriterInput);
NSParameterAssert([videoWriter canAddInput:audioWriterInput]);
audioWriterInput.expectsMediaDataInRealTime = NO;
[videoWriter addInput:audioWriterInput];
[videoWriter startWriting];
[videoWriter startSessionAtSourceTime:kCMTimeZero];
[reader startReading];
dispatch_queue_t _processingQueue = dispatch_queue_create("assetAudioWriterQueue", NULL);
[videoWriterInput requestMediaDataWhenReadyOnQueue:_processingQueue usingBlock:
^{
[self retain];
while ([videoWriterInput isReadyForMoreMediaData]) {
CMSampleBufferRef sampleBuffer;
if ([reader status] == AVAssetReaderStatusReading &&
(sampleBuffer = [asset_reader_output copyNextSampleBuffer])) {
BOOL result = [videoWriterInput appendSampleBuffer:sampleBuffer];
CFRelease(sampleBuffer);
if (!result) {
[reader cancelReading];
break;
}
} else {
[videoWriterInput markAsFinished];
switch ([reader status]) {
case AVAssetReaderStatusReading:
// the reader has more for other tracks, even if this one is done
break;
case AVAssetReaderStatusCompleted:
// your method for when the conversion is done
// should call finishWriting on the writer
//hook up audio track
[audioReader startReading];
[videoWriter startSessionAtSourceTime:kCMTimeZero];
dispatch_queue_t mediaInputQueue = dispatch_queue_create("mediaInputQueue", NULL);
[audioWriterInput requestMediaDataWhenReadyOnQueue:mediaInputQueue usingBlock:^
{
NSLog(@"Request");
NSLog(@"Asset Writer ready :%d",audioWriterInput.readyForMoreMediaData);
while (audioWriterInput.readyForMoreMediaData) {
CMSampleBufferRef nextBuffer;
if ([audioReader status] == AVAssetReaderStatusReading &&
(nextBuffer = [readerOutput copyNextSampleBuffer])) {
NSLog(@"Ready");
if (nextBuffer) {
NSLog(@"NextBuffer");
[audioWriterInput appendSampleBuffer:nextBuffer];
}
}else{
[audioWriterInput markAsFinished];
switch ([audioReader status]) {
case AVAssetReaderStatusCompleted:
[videoWriter finishWriting];
[self hookUpVideo:newName];
break;
}
}
}
}
];
break;
case AVAssetReaderStatusFailed:
[videoWriter cancelWriting];
break;
}
break;
}
}
}
];
NSLog(@"Write Ended");
}
不幸的是，如果我传入的视频超过 2 秒，该应用程序会疯狂地占用内存并崩溃！代码看起来相当简单，但我似乎无法让它工作！
我应该在写入后在某处释放缓冲区吗?我会非常感谢任何有意见的人.
Unfortunately, if I pass in a video any longer than 2 seconds, the app sucks up memory like crazy and crashes! The code seems fairly simple, but I cannot seem to get it to work!
Am I supposed to release the buffer in there somewhere after it is written? I would be most greatful to anyone that has any input.
推荐答案
-copyNextSampleBuffer 返回一个 CMSampleBufferRef 和 +1 保留(复制方法这样做).这意味着您必须释放对象.由于您没有这样做，因此每次通过 while() 循环时都会泄漏一个副本.
-copyNextSampleBuffer is returning a CMSampleBufferRef with +1 retain (copy methods do that). This means you must release the object. Since you're not doing so, you're going to leak a copy every pass through your while() loop.
此外，您在没有管理自动释放池的情况下紧密地运行该循环.如果在您调用的任何例程中自动释放对象，则在您上方的自动释放池耗尽之前，它们不会被释放.由于您的 while() 循环持续时间基于输入，因此非常适合添加手动自动释放池.
Additionally, you're running that loop tightly without managing an autorelease pool. If there are objects being autoreleased in any of the routines you're calling, they will not be released until the autorelease pool above you drains. Since your while() loop duration is based on input, it's a good candidate for adding a manual autorelease pool.
要考虑的另一件事:因为您使用 while() 循环同步运行它，您将阻塞线程并可能在继续条件上不必要地旋转几次.AVAssetWriterInput 提供了一种替代机制来使用 libdispatch 在资源可用时异步处理数据:-requestMediaDataWhenReadyOnQueue:usingBlock:
One other thing to consider: because you're running this synchronously with a while() loop, you'll block the thread and possibly spin unnecessarily over your continue condition several times. AVAssetWriterInput provides an alternative mechanism to use libdispatch to process data asynchronously as resources become available: -requestMediaDataWhenReadyOnQueue:usingBlock:
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