P2P优化

简介

m3u8的配置(或者mpd)对P2P效果会产生很大的影响，适当的配置（包括每个切片的时长和每个m3u8/mpd包含的切片数量等）可以显著提高P2P率。建议不要使用多码率m3u8/mpd。

直播模式m3u8/mpd参考配置

• 切片时长：3到4秒
• 每个m3u8/mpd切片数量：不少于10个

以NGINX为例:

rtmp {
    server {
        ...
        application show {
            ...
            hls_fragment 4;                # 4 seconds fragments
            hls_playlist_length 60;        # 60 seconds playlist
        }
    }
}

允许Http Range请求

Http Range请求用于下载指定范围的数据，可以在一部分数据已用P2P下载的情况下，剩余部分用http下载补足。如果从对等端P2P下载速度较慢，那么在达到超时时间后，就可以把剩余数据交给http range请求下载，而不需要重新完整下载整个数据，从而节省CDN的带宽，下图阐述了不采用和采用Http Range的区别：

要启动Http Range请求，需要同时在源服务器和CDN开启OPTIONS和RANGE请求：(Native端不需要开启OPTIONS)

OPTIONS请求

OPTIONS请求是浏览器在跨域情况下发起Range请求之前的预检请求，一般只需要配置服务器使Http头有以下响应：(安卓和iOS不需要配置)

Access-Control-Allow-Methods: GET, OPTIONS

RANGE请求

要开启RANGE请求，一般只需要配置服务器使Http头有以下响应：

Access-Control-Allow-Headers: Range

NGINX 示例

add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
add_header 'Access-Control-Allow-Headers' 'Range';
add_header 'Access-Control-Allow-Origin' '*';
# allow CORS preflight requests
if ($request_method = 'OPTIONS') {
    add_header 'Access-Control-Allow-Headers' 'Range';
    add_header 'Access-Control-Max-Age' 1728000;
    add_header 'Content-Type' 'text/plain charset=UTF-8';
    add_header 'Content-Length' 0;
    return 204;
}

将播放缓冲信息回调给SDK

由于P2P采用本地代理服务器模式，SDK与播放器解耦，无法获取播放器的播放信息。建议在直播或者MP4播放模式下，通过SDK提供的接口 ，将播放器从当前播放时间到缓冲前沿的时间间隔回调给SDK。

安卓ExoPlayer示例

import com.cdnbye.core.p2p.PlayerInteractor;
P2pEngine.getInstance().setPlayerInteractor(new PlayerInteractor() {
    @Override
    public long onBufferedDuration() {
        // Exoplayer 单位：毫秒
        return player.getBufferedPosition() - player.getCurrentPosition();
    }
});

iOS AVPlayer示例

@interface ViewController () <CBP2pEngineDelegate>
...
[CBP2pEngine sharedInstance].delegate = self;
NSURL *parsedUrl = [[CBP2pEngine sharedInstance] parseStreamURL:ORIGINAL_URL];
AVPlayerItem *playerItem =[[AVPlayerItem alloc] initWithURL: parsedUrl];
self.player = [[AVPlayer alloc] initWithPlayerItem: playerItem];
...
#pragma mark - **************** CBP2pEngineDelegate ****************
-(NSTimeInterval)bufferedDuration {
    NSTimeInterval currentTime = CMTimeGetSeconds([self.player currentTime]);
    NSTimeInterval bufferedDuration = 0;
    for (NSValue *value in [[self.player currentItem] loadedTimeRanges]) {
        CMTimeRange timeRange = [value CMTimeRangeValue];
        NSTimeInterval start = CMTimeGetSeconds(timeRange.start);
        NSTimeInterval end = start + CMTimeGetSeconds(timeRange.duration);
        if (currentTime >= start && currentTime <= end) {
            bufferedDuration = end - currentTime;         // 单位：秒
            break;
        }
    }
    return bufferedDuration;
}

设置播放缓冲策略

限制播放器缓冲大小，可以达到更好的P2P效果，以下参数请根据实际情况进行调整。

安卓ExoPlayer示例

class VideoPlayerConfig {
    //Minimum Video you want to buffer while Playing
    public static final int MIN_BUFFER_DURATION = 7000;
    //Max Video you want to buffer during PlayBack
    public static final int MAX_BUFFER_DURATION = 15000;
    //Min Video you want to buffer before start Playing it
    public static final int MIN_PLAYBACK_START_BUFFER = 7000;
    //Min video You want to buffer when user resumes video
    public static final int MIN_PLAYBACK_RESUME_BUFFER = 7000;
}
// Create LoadControl
LoadControl loadControl = new DefaultLoadControl.Builder()
        .setAllocator(new DefaultAllocator(true, 16))
        .setBufferDurationsMs(VideoPlayerConfig.MIN_BUFFER_DURATION,
                VideoPlayerConfig.MAX_BUFFER_DURATION,
                VideoPlayerConfig.MIN_PLAYBACK_START_BUFFER,
                VideoPlayerConfig.MIN_PLAYBACK_RESUME_BUFFER)
        .setTargetBufferBytes(-1)
        .setPrioritizeTimeOverSizeThresholds(true).createDefaultLoadControl();
// Create a player instance.
player = ExoPlayerFactory.newSimpleInstance(this, new DefaultTrackSelector(), loadControl);