我正在尝试处理本地视频文件，只是对像素数据进行一些分析。什么都没有输出。
我当前的代码遍历视频的每一帧，但实际上我希望一次跳过~15帧以加快速度。有没有办法跳过帧而不解码它们？
在Ffmpeg中，我只需调用av_read_frame而无需调用avcodec_decode_video2。
谢谢！这是我目前的代码：
- (void) readMovie:(NSURL *)url
{
[self performSelectorOnMainThread:@selector(updateInfo:) withObject:@"scanning" waitUntilDone:YES];
startTime = [NSDate date];
AVURLAsset * asset = [AVURLAsset URLAssetWithURL:url options:nil];
[asset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:@"tracks"] completionHandler:
^{
dispatch_async(dispatch_get_main_queue(),
^{
AVAssetTrack * videoTrack = nil;
NSArray * tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
if ([tracks count] == 1)
{
videoTrack = [tracks objectAtIndex:0];
videoDuration = CMTimeGetSeconds([videoTrack timeRange].duration);
NSError * error = nil;
// _movieReader is a member variable
_movieReader = [[AVAssetReader alloc] initWithAsset:asset error:&error];
if (error)
NSLog(@"%@", error.localizedDescription);
NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey;
NSNumber* value = [NSNumber numberWithUnsignedInt: kCVPixelFormatType_32BGRA];
NSDictionary* videoSettings = [NSDictionary dictionaryWithObject:value forKey:key];
AVAssetReaderTrackOutput* output = [AVAssetReaderTrackOutput
assetReaderTrackOutputWithTrack:videoTrack
outputSettings:videoSettings];
output.alwaysCopiesSampleData = NO;
[_movieReader addOutput:output];
if ([_movieReader startReading])
{
NSLog(@"reading started");
[self readNextMovieFrame];
}
else
{
NSLog(@"reading can't be started");
}
}
});
}];
}
- (void) readNextMovieFrame
{
//NSLog(@"readNextMovieFrame called");
if (_movieReader.status == AVAssetReaderStatusReading)
{
//NSLog(@"status is reading");
AVAssetReaderTrackOutput * output = [_movieReader.outputs objectAtIndex:0];
CMSampleBufferRef sampleBuffer = [output copyNextSampleBuffer]; // this is the most expensive call
if (sampleBuffer)
{
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
// Lock the image buffer
CVPixelBufferLockBaseAddress(imageBuffer,0);
// Get information of the image
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
//
// Here's where you can process the buffer!
// (your code goes here)
//
// Finish processing the buffer!
//
// Unlock the image buffer
CVPixelBufferUnlockBaseAddress(imageBuffer,0);
CFRelease(sampleBuffer);
[self readNextMovieFrame];
}
else
{
NSLog(@"could not copy next sample buffer. status is %d", _movieReader.status);
NSTimeInterval scanDuration = -[startTime timeIntervalSinceNow];
float scanMultiplier = videoDuration / scanDuration;
NSString* info = [NSString stringWithFormat:@"Done\n\nvideo duration: %f seconds\nscan duration: %f seconds\nmultiplier: %f", videoDuration, scanDuration, scanMultiplier];
[self performSelectorOnMainThread:@selector(updateInfo:) withObject:info waitUntilDone:YES];
}
}
else
{
NSLog(@"status is now %d", _movieReader.status);
}
}
- (void) updateInfo: (id*)message
{
NSString* info = [NSString stringWithFormat:@"%@", message];
[infoTextView setText:info];
}
答案 0 :(得分：0)
只需在代码中添加bool值
- (void) readMovie:(NSURL *)url
{
[self performSelectorOnMainThread:@selector(updateInfo:) withObject:@"scanning" waitUntilDone:YES];
startTime = [NSDate date];
AVURLAsset * asset = [AVURLAsset URLAssetWithURL:url options:nil];
[asset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:@"tracks"] completionHandler:
^{
dispatch_async(dispatch_get_main_queue(),
^{
AVAssetTrack * videoTrack = nil;
NSArray * tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
if ([tracks count] == 1)
{
videoTrack = [tracks objectAtIndex:0];
videoDuration = CMTimeGetSeconds([videoTrack timeRange].duration);
NSError * error = nil;
// _movieReader is a member variable
_movieReader = [[AVAssetReader alloc] initWithAsset:asset error:&error];
if (error)
NSLog(@"%@", error.localizedDescription);
NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey;
NSNumber* value = [NSNumber numberWithUnsignedInt: kCVPixelFormatType_32BGRA];
NSDictionary* videoSettings = [NSDictionary dictionaryWithObject:value forKey:key];
AVAssetReaderTrackOutput* output = [AVAssetReaderTrackOutput
assetReaderTrackOutputWithTrack:videoTrack
outputSettings:videoSettings];
output.alwaysCopiesSampleData = NO;
[_movieReader addOutput:output];
if ([_movieReader startReading])
{
NSLog(@"reading started");
[self readNextMovieFrame];
}
else
{
NSLog(@"reading can't be started");
}
}
});
}];
}
BOOL skipFrame = FALSE;
- (void) readNextMovieFrame
{
//NSLog(@"readNextMovieFrame called");
if (_movieReader.status == AVAssetReaderStatusReading)
{
//NSLog(@"status is reading");
AVAssetReaderTrackOutput * output = [_movieReader.outputs objectAtIndex:0];
CMSampleBufferRef sampleBuffer = [output copyNextSampleBuffer];
if (sampleBuffer && !skipFrame)
{
skipFrame = TRUE;
// I'm guessing this is the expensive part that we can skip if we want to skip frames
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
// Lock the image buffer
CVPixelBufferLockBaseAddress(imageBuffer,0);
// Get information of the image
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
//
// Here's where you can process the buffer!
// (your code goes here)
//
// Finish processing the buffer!
//
// Unlock the image buffer
CVPixelBufferUnlockBaseAddress(imageBuffer,0);
CFRelease(sampleBuffer);
}
else
{
skipFrame = FALSE;
NSLog(@"could not copy next sample buffer. status is %d", _movieReader.status);
NSTimeInterval scanDuration = -[startTime timeIntervalSinceNow];
float scanMultiplier = videoDuration / scanDuration;
NSString* info = [NSString stringWithFormat:@"Done\n\nvideo duration: %f seconds\nscan duration: %f seconds\nmultiplier: %f", videoDuration, scanDuration, scanMultiplier];
[self performSelectorOnMainThread:@selector(updateInfo:) withObject:info waitUntilDone:YES];
}
[self readNextMovieFrame];
}
else
{
NSLog(@"status is now %d", _movieReader.status);
}
}
- (void) updateInfo: (id*)message
{
NSString* info = [NSString stringWithFormat:@"%@", message];
[infoTextView setText:info];
}