我是AVFoundation和解码过程的新手。我需要解码一个H264视频文件并在iPhone上播放它...有人可以给我指导吗。
我不想使用任何第三方库(例如ffmpeg)来完成这项工作。据我所知,使用AVFoundation编码是可能的...这里是我认为用于编码的代码,但并不确定...
float bitsPerPixel;
CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions(currentFormatDescription);
int numPixels = dimensions.width * dimensions.height;
int bitsPerSecond;
// Assume that lower-than-SD resolutions are intended for streaming, and use a lower bitrate
if ( numPixels < (640 * 480) )
bitsPerPixel = 4.05; // This bitrate matches the quality produced by AVCaptureSessionPresetMedium or Low.
else
bitsPerPixel = 11.4; // This bitrate matches the quality produced by AVCaptureSessionPresetHigh.
bitsPerSecond = numPixels * bitsPerPixel;
NSDictionary *videoCompressionSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoCodecH264, AVVideoCodecKey,
[NSNumber numberWithInteger:dimensions.width], AVVideoWidthKey,
[NSNumber numberWithInteger:dimensions.height], AVVideoHeightKey,
[NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInteger:bitsPerSecond], AVVideoAverageBitRateKey,
[NSNumber numberWithInteger:30], AVVideoMaxKeyFrameIntervalKey,
nil], AVVideoCompressionPropertiesKey,
nil];
if ([assetWriter canApplyOutputSettings:videoCompressionSettings forMediaType:AVMediaTypeVideo]) {
assetWriterVideoIn = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo outputSettings:videoCompressionSettings];
assetWriterVideoIn.expectsMediaDataInRealTime = YES;
assetWriterVideoIn.transform = [self transformFromCurrentVideoOrientationToOrientation:self.referenceOrientation];
if ([assetWriter canAddInput:assetWriterVideoIn])
[assetWriter addInput:assetWriterVideoIn];
else {
NSLog(@"Couldn't add asset writer video input.");
return NO;
}
}
else {
NSLog(@"Couldn't apply video output settings.");
return NO;
}
return YES;
我对此完全不了解,请帮忙...从哪里开始?
谢谢