无法导出AVPlayerItem [英] Unable to export AVPlayerItem
问题描述
我正在使用AVQueuePlayer播放我们应用中的视频列表.我正在尝试缓存AVQueuePlayer播放的视频，以便不必每次都下载视频.
I'm using AVQueuePlayer to do playback of a list of videos in our app. I'm trying to cache the videos that are played by AVQueuePlayer so that the video doesn't have to be downloaded each time.
因此，在视频播放完毕后，我尝试将AVPlayerItem保存到磁盘，以便下次使用本地URL对其进行初始化.
So, after the video finishes playing, I attempt to save the AVPlayerItem into disk so next time it's initialized with a local URL.
我试图通过两种方法来实现这一目标:
I've tried to achieve this through two approaches:
- 使用AVAssetExportSession
- 使用AVAssetReader和AVAssetWriter.
1)AVAssetExportSession方法
这种方法是这样的:
1) AVAssetExportSession approach
This approach works like this:
- 在
AVPlayerItem使用AVPlayerItemDidPlayToEndTimeNotification完成播放时进行观察. - 收到上述通知(视频已播放完毕，因此已完全下载)，请使用
AVAssetExportSession将该视频导出到磁盘中的文件中.
- Observe when an
AVPlayerItemfinishes playing usingAVPlayerItemDidPlayToEndTimeNotification. - When the above notification is received (a video finished playing, so it's fully downloaded), use
AVAssetExportSessionto export that video into a file in disk.
代码:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(videoDidFinishPlaying:) name:AVPlayerItemDidPlayToEndTimeNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(videoDidFinishPlaying:) name:AVPlayerItemDidPlayToEndTimeNotification object:nil];
然后
- (void)videoDidFinishPlaying:(NSNotification*)note
{
AVPlayerItem *itemToSave = [note object];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:itemToSave.asset presetName:AVAssetExportPresetHighestQuality];
exportSession.outputFileType = AVFileTypeMPEG4;
exportSession.outputURL = [NSURL fileURLWithPath:@"/path/to/Documents/video.mp4"];
[exportSession exportAsynchronouslyWithCompletionHandler:^{
switch(exportSession.status){
case AVAssetExportSessionStatusExporting:
NSLog(@"Exporting...");
break;
case AVAssetExportSessionStatusCompleted:
NSLog(@"Export completed, wohooo!!");
break;
case AVAssetExportSessionStatusWaiting:
NSLog(@"Waiting...");
break;
case AVAssetExportSessionStatusFailed:
NSLog(@"Failed with error: %@", exportSession.error);
break;
}
}
- (void)videoDidFinishPlaying:(NSNotification*)note
{
AVPlayerItem *itemToSave = [note object];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:itemToSave.asset presetName:AVAssetExportPresetHighestQuality];
exportSession.outputFileType = AVFileTypeMPEG4;
exportSession.outputURL = [NSURL fileURLWithPath:@"/path/to/Documents/video.mp4"];
[exportSession exportAsynchronouslyWithCompletionHandler:^{
switch(exportSession.status){
case AVAssetExportSessionStatusExporting:
NSLog(@"Exporting...");
break;
case AVAssetExportSessionStatusCompleted:
NSLog(@"Export completed, wohooo!!");
break;
case AVAssetExportSessionStatusWaiting:
NSLog(@"Waiting...");
break;
case AVAssetExportSessionStatusFailed:
NSLog(@"Failed with error: %@", exportSession.error);
break;
}
}
该代码在控制台中的结果是:
The result in console of that code is:
Failed with error: Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo=0x98916a0 {NSLocalizedDescription=The operation could not be completed, NSUnderlyingError=0x99ddd10 "The operation couldn’t be completed. (OSStatus error -12109.)", NSLocalizedFailureReason=An unknown error occurred (-12109)}
2)AVAssetReader，AVAssetWriter方法
代码:
- (void)savePlayerItem:(AVPlayerItem*)item
{
NSError *assetReaderError = nil;
AVAssetReader *assetReader = [[AVAssetReader alloc] initWithAsset:assetToCache error:&assetReaderError];
//(algorithm continues)
}
- (void)savePlayerItem:(AVPlayerItem*)item
{
NSError *assetReaderError = nil;
AVAssetReader *assetReader = [[AVAssetReader alloc] initWithAsset:assetToCache error:&assetReaderError];
//(algorithm continues)
}
当尝试使用以下信息分配/初始化AVAssetReader时，该代码引发异常:
That code throws an exception when trying to alloc/init the AVAssetReader with the following information:
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[AVAssetReader initWithAsset:error:] Cannot initialize an instance of AVAssetReader with an asset at non-local URL 'https://someserver.com/video1.mp4''
***
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[AVAssetReader initWithAsset:error:] Cannot initialize an instance of AVAssetReader with an asset at non-local URL 'https://someserver.com/video1.mp4''
***
非常感谢您的帮助.
推荐答案
我最终设法做到的是创建通常由AVPlayer> AVPlayerItem> AVURLAsset组成的数组.但同时，在AVPlayer从远程URL完全加载视频之前，立即创建AVExportSession.
How I ended up manage to do this is to create the usually array of AVPlayer > AVPlayerItem > AVURLAsset. But also at the same time create an AVExportSession right away before AVPlayer have completely loaded the video from the remote URL.
当AVPlayer尝试预缓冲URL时，AVExportSession实际上将缓慢导出.这与用户是否开始播放AVPlayer无关.但是，只有预先缓冲了整个URL之后，输出文件才能真正完成.届时AVExportSession将随着完成情况回调.这也完全独立于用户是否正在播放视频或是否已经播放完视频.
The AVExportSession actually will export slowly as the AVPlayer tries to pre-buffer the URL. This is irregardless of whether the user starts playing the AVPlayer or not. However the output file will not actually complete until the entire URL is pre-buffered. At that point AVExportSession will callback with the completion. This is also completely independent of whether the user is playing, or have completed playing the video or not.
因此，通过尽早创建AVPlayer/AVExportSession组合，它成为了我的预缓冲机制
As such by creating the AVPlayer/AVExportSession combo early, it became my pre-buffer mechanism
-更新2018-01-10-
-- Update 2018-01-10 --
想要在部署了上述机制之后添加它.我们遇到了1个重要警告，我认为值得一提.
Want to add that after having deployed the above mechanism. We have encountered 1 big caveat that I think deserves some mention.
内存中不能有太多视频管道(已连接AVPlayerItem/AVAsset的AVPlayer). AVFoundation将拒绝播放.因此，请使用上述机制进行预缓冲.但是将视频下载到文件后，如果用户不观看视频，请取消分配AVPlayer/AVAsset.当用户决定再次播放视频时，这次重新分配AVPlayer，这次AVURLAsset指向视频的本地缓冲副本.
You cannot have too many video pipelines in memory (AVPlayer with AVPlayerItem/AVAsset hooked up). AVFoundation will refusing to play. So do use the above mechanism to pre-buffer. But once the video is downloaded to a file, if the user is not viewing the video, dealloc the AVPlayer/AVAsset. Reallocate an AVPlayer when the user decides to play the video again, this time with the AVURLAsset pointed to your local buffered copy of the video.
这篇关于无法导出AVPlayerItem的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
