m3u8 file AVAssetImageGenerator error

问题:

I am using AVPlayer to play .m3u8 file. Using AVAssetImageGenerator to extract image out of it using following code :

AVURLAsset *asset1 = [[AVURLAsset alloc] initWithURL:mp.contentURL options:nil];
AVAssetImageGenerator *generate1 = [[AVAssetImageGenerator alloc] initWithAsset:asset1];
generate1.appliesPreferredTrackTransform = YES;
NSError *err = NULL;
CMTime time = CMTimeMake(1, 2);
CGImageRef oneRef = [generate1 copyCGImageAtTime:time actualTime:NULL error:&err];
img = [[UIImage alloc] initWithCGImage:oneRef];

It always gives me error :

Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo=0x7fb4e30cbfa0 {NSUnderlyingError=0x7fb4e0e28530 "The operation couldn’t be completed. (OSStatus error -12782.)", NSLocalizedFailureReason=An unknown error occurred (-12782), NSLocalizedDescription=The operation could not be completed}

It works for mp4,mov and all major video extensions URL but not for m3u8. Any idea??

回答1:

Your problem is only to be expected. .m3u8 Files are not actual Asset files, rather, they are more akin to a playlist. They are used in HTTP Live Streaming and provide a location for "Segments" based on available bandwidth.

here is an example of a .m3u8 file (Apple's sample .m3u8 file)

#EXTM3U
#EXT-X-STREAM-INF:PROGRAM-ID=1, BANDWIDTH=200000
gear1/prog_index.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1, BANDWIDTH=311111
gear2/prog_index.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1, BANDWIDTH=484444
gear3/prog_index.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1, BANDWIDTH=737777
gear4/prog_index.m3u8

Unfortunately, you can not create an AVAsset or AVURLAsset to represent the media in a HTTP Live stream. Reference:Apple's reference example of Asset Loading/playing

回答2:

You won't be able to get still images for a live stream using AVAssetImageGenerator. Instead, you can use

AVPlayerItemVideoOutput

With AVPlayerItemVideoOutput you can get an image that is appropriate to display at a specified time for a given .m3u8 stream using the following method: - (CVPixelBufferRef)copyPixelBufferForItemTime:(CMTime)itemTime itemTimeForDisplay:(CMTime *)outItemTimeForDisplay Then, you can convert the returned CVPixelBufferRef into an image (or other) for display.

回答3:

our finding is that, if you play a HLS stream which has "I-Frame only playlist", for example stream “https://tungsten.aaplimg.com/VOD/bipbop_adv_example_v2/master.m3u8”(has I-frame only playlist), AVAssetImageGenerator could generate the requested image one by one.

But please notice that "it is only fine on iOS8.X and iOS9.X", but failed at iOS10.X.

I have committed a bug report to Apple Bug Reporter.