http://blog.csdn.net/yqxh_wang/article/details/49477131
M3U8是一种流媒体,现多用于视频播放。当把m3u8格式视频的url下载下来用文本打开会发现其实只是一段字符串,包含了很多视频小片段的地址,那么怎么样把整个视频下载下来用于本地播放呢?
首先,m3u8展开后的字符串类似这样:
http://f.youku.com/player/getMpegtsPath/st/flv/fileid/03000201004F4BC6AFD0C202E26EEEB41666A0-C93C-D6C9-9FFA-33424A776707/ipad0_0.ts?KM=14eb49fe4969126c6&start=0&end=10&ts=10&html5=1&seg_no=0&seg_time=0 http://f.youku.com/player/getMpegtsPath/st/flv/fileid/03000201004F4BC6AFD0C202E26EEEB41666A0-C93C-D6C9-9FFA-33424A776707/ipad0_1.ts?KM=14eb49fe4969126c6&start=10&end=30&ts=20&html5=1&seg_no=1&seg_time=0 http://f.youku.com/player/getMpegtsPath/st/flv/fileid/03000201004F4BC6AFD0C202E26EEEB41666A0-C93C-D6C9-9FFA-33424A776707/ipad0_2.ts?KM=14eb49fe4969126c6&start=30&end=50&ts=20&html5=1&seg_no=2&seg_time=0 http://f.youku.com/player/getMpegtsPath/st/flv/fileid/03000201004F4BC6AFD0C202E26EEEB41666A0-C93C-D6C9-9FFA-33424A776707/ipad0_3.ts?KM=14eb49fe4969126c6&start=50&end=70&ts=20&html5=1&seg_no=3&seg_time=0 http://f.youku.com/player/getMpegtsPath/st/flv/fileid/03000201004F4BC6AFD0C202E26EEEB41666A0-C93C-D6C9-9FFA-33424A776707/ipad0_4.ts?KM=14eb49fe4969126c6&start=70&end=98&ts=24&html5=1&seg_no=4&seg_time=0
在每一行#EXTINF:下面的网址就是一个个ts文件的地址,实际去下载的是这些小片段。而在#EXTINF:后面的数字代表的是这个ts文件所包含视频的时长。
所以第一步要解析这个m3u8的url,将其中所有ts文件的下载地址记录下来:
NSString *data = [NSString stringWithContentsOfURL:url usedEncoding:&encoding error:&error];NSMutableArray *segments = [NSMutableArray array];NSRange segmentRange = [remainData rangeOfString:@"#EXTINF:"];NSInteger segmentIndex = 0;NSInteger totalSeconds = 0;while (segmentRange.location != NSNotFound) { SCM3U8SegmentInfo *segment = [[SCM3U8SegmentInfo alloc] init]; NSRange commaRange = [remainData rangeOfString:@","]; NSString *value = [remainData substringWithRange:NSMakeRange(segmentRange.location + [@"#EXTINF:" length], commaRange.location -(segmentRange.location + [@"#EXTINF:" length]))]; segment.duration = [value intValue]; totalSeconds+=segment.duration; remainData = [remainData substringFromIndex:commaRange.location]; NSRange linkRangeBegin = [remainData rangeOfString:@"http"]; NSRange linkRangeEnd = [remainData rangeOfString:@"#"]; NSString *linkurl = [remainData substringWithRange:NSMakeRange(linkRangeBegin.location, linkRangeEnd.location - linkRangeBegin.location)]; segment.url = linkurl; segment.index = segmentIndex; segmentIndex++; [segments addObject:segment]; remainData = [remainData substringFromIndex:linkRangeEnd.location]; segmentRange = [remainData rangeOfString:@"#EXTINF:"];}
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然后得到了这些文件的地址后,就可以去下载了。下载方法有很多,可以用NSURLConnection,NSURLSession,ASIHTTPRequest,AFNetworking等。注意因为一个视频包含很多个小的ts文件,所以为了便于管理,建议1 是将这些文件按索引号分别命名为id0.ts,id1.ts,id2.ts等,2 是按顺序去下载这些小片段,且同一时间只下载一个,当一个下载完成后,再去下载下一个。
接着当所有这些ts文件下载完成后,需要将它们在本地拼接成一个新的m3u8文件:
NSString *pathPrefix = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES) objectAtIndex:0];NSString *saveTo = [[pathPrefix stringByAppendingPathComponent:kPathDownload] stringByAppendingPathComponent:self.vid];NSString *fullPath = [saveTo stringByAppendingPathComponent:@"movie.m3u8"];NSString* head = @"#EXTM3U\n#EXT-X-TARGETDURATION:30\n#EXT-X-VERSION:2\n#EXT-X-DISCONTINUITY\n";NSString* segmentPrefix = [NSString stringWithFormat:@"http://127.0.0.1:54321/%@/",self.vid];NSInteger count = [self.segmentList.segments count];for(int i = 0;i<count;i++){ NSString *filename = [NSString stringWithFormat:@"id%d.ts",i]; SCM3U8SegmentInfo *segInfo = [self.segmentList getSegmentWithIndex:i]; NSString *length = [NSString stringWithFormat:@"#EXTINF:%ld,\n",(long)segInfo.duration]; NSString *url = [segmentPrefix stringByAppendingString:filename]; head = [NSString stringWithFormat:@"%@%@%@\n",head,length,url];}NSString* end = @"#EXT-X-ENDLIST";head = [head stringByAppendingString:end];NSMutableData *writer = [[NSMutableData alloc] init];[writer appendData:[head dataUsingEncoding:NSUTF8StringEncoding]];[writer writeToFile:fullPath atomically:YES];
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其中http://127.0.0.1是随便写的,只要和播放时调用的一致即可。拼成后本地的m3u8文件用文本打开类似如下
#EXTM3U#EXT-X-TARGETDURATION:30#EXT-X-VERSION:2#EXT-X-DISCONTINUITY#EXTINF:6,http:#EXTINF:6,http:#EXTINF:6,http:#EXTINF:6,http:#EXTINF:6,http:#EXTINF:6,http:#EXTINF:6,http:#EXTINF:6,http:#EXTINF:6,http:#EXT-X-ENDLIST
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最后由于m3u8只支持http协议的远程播放,所以必须在应用程序里搭建一个服务器。好消息是早就有开源库CocoaHTTPServer做到了这一点
- (void)setHttpServer{ _httpServer = [[HTTPServer alloc] init]; [_httpServer setType:@"_http._tcp."]; [_httpServer setPort:54321]; NSString *pathPrefix = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES) objectAtIndex:0]; NSString *webPath = [pathPrefix stringByAppendingPathComponent:kPathDownload]; NSLog(@"Setting document root: %@", webPath); [_httpServer setDocumentRoot:webPath]; NSError *error; if(![_httpServer start:&error]) { NSLog(@"Error starting HTTP Server: %@", error); }}
综上,将类似@”http://127.0.0.1:54321/%@/movie.m3u8“这样的地址传给你的播放器就可以实现本地播放了。
完整项目地址为 https://github.com/wangqi211/M3U8VideoDownloadDemo