hls-p2p

Flash OSMF based hybrid cdn&p2p hls solution. Currently it support LIVE hls. Flash support rtmfp protocal, we use that to deliver video&audio data in p2p&cdn hybrid way.

NOTE: Please take some time to READ this file.

how it works

We use https://github.com/denivip/osmf-hls-plugin to enable hls support. Use that as a base, we developed the p2p part.

Normally, for hls protocal, client download m3u8 first, then download ts; In our p2p solution, client download m3u8 from server first, then download ts and m3u8 from server or other peers.

We developed a algorithm for LIVE hls P2P.

The algorithm is like this:

• for a single ts file, if we download it from peer, we download it from more than one peer
• we establish a p2p topology at first.
• data is pushed from one peer to others
• if one peer exits, downstream will know that after a while, and will PING the exited peer, if PING fails, it will retry to establising a new topology. In the process of rebuilding the new topology, data will be downloaded from server.
• peer is considered as stable if it can be added to other peer's topology.
• m3u8 is small, it will be downloaded only from one peer.

Server part:

• P2P need a server to support rtmfp. we use https://github.com/OpenRTMFP/Cumulus. Cumulus support lua, we can add peer id to redis using lua script.
• we also use redis to store peer ids.
• a nodejs http service for peer to find other peers' id.

Client part:

• we implement a P2PLoader, which will replace the original HTTPStreamDownloader in osmf-hls-plugin

Install

• our test server is CentOS 6.2, you can bash install/install_p2p.sh to install required server software.
• The IDE we used to develope our flash code is 'FlashDevelop'

Run and test

Server:

• start redis
• copy "cumulus/main.lua" to "Cumulus/CumulusServer/www" folder and start CumulusServer. For how to set config for CumulusServer, refer to https://github.com/OpenRTMFP/Cumulus/wiki/Installation#configurations
• copy "server/remote_log" to any folder, under remote_log, run npm install, then node index.js
• you also need a media server to stream HLS(such as FMS, Wowza, or Lava Media Server 4(trochilus) if you interested). note: Lava Media Server 4 is not a open source project now.

Client:

• Build the binary. Note: because we use osmf source code directly, you need to remove default osmf lib in you computer before building it.
• Change config in bin/index.html

change the ip of your server in bin/index.html, such as "115.29.205.140"

some config value and their meanings are as follows:

# the url of LIVE hls stream, it MUST be live and single stream
# it should only contain ts file, and MUST NOT contain another m3u8 file
m3u8_url: "http://211.103.128.226:8080/live/tvie/xray/pad.m3u8",
# the rtmfp url
rtmfp_url: "rtmfp://115.29.205.140:19350/app",
# the url we will get peers information
http_tracker: "http://115.29.205.140:5000/get_peers",
# send log to that url
remote_log_base_url: "http://115.29.205.140:5000/remote_log",
# how many peers we will use to download data
rtmfp_url_peers: 2,
# leave it as it is
index_rtmfp_url: "",
# leave it as it is
index_rtmfp_url_peers: 1,
# the server ip and port from where we download m3u8 and ts.
# if you do not know how it works, set it as the same as `m3u8_url`
source_servers: ["211.103.128.226:8080"]

• put bin/* under a web server(such as nginx).
• visit bin/index.html in your browser

Data

In Cumulus, we will add peer informations to redis. You can get the peer informations in redis with following command

• List all p2p instance.

127.0.0.1:6379 > SMEMBERS cumulus_app

• For one p2p instance, get all connected peers' id. for example: if I want to get peers of a p2p instance called "app"

127.0.0.1:6379> LLEN app
(integer) 1
127.0.0.1:6379> LRANGE app 0 1
1) "c39e1de52e704279ecb6800bdb4c20006059d6b600b8abd08941a4119dc4250b"

• For some debug reason, if you want to clear all peers of a p2p instance called "app", you can do

127.0.0.1:6379> LTRIM app 0 0

peer - server protocal

• Flash client connect Cumulus using RTMFP protocal. Flash client will get a peerID(a unique id), and in main.lua, we save client peerID to redis.
• Flash client send http request to remote_log service to find other peer ids, so that it can connect other peer.
• If user close the index.html page, the page will send disconnect event to remote_log, remote_log will remove that peer's id from redis.(We need to do this because Flash in chrome will not send disconnect event to Cumulus server)

peers protocal

• First, we need to create two way session between two peer, from each side it can send msg. We call it "Create Session"
• We call one ts file as CHUNK. A CHUNK may contain more than one PIECE. We download one PIECE of CHUNK from different peer.
• After we have connect ENOUGH peers, we send them HAS_CHUNK_REQ(ts_url) msg to query if we can download PIECE from them.
• After enough peers send back us 'HAS_CHUNK_RESP(yes)', We send 'GET_PIECE_REQ(url, piece_id)' to qualified peers.
• After we got some data of a CHUNK, we feed it to player.
• If we do not get the CHUNK at required time, we will query if the peer still alive, if not, we call it "P2P Failed".
• If we are in "P2P Failed", we will shift from "P2P mode" to "CDN mode".
• If we are in "CDN mode", we will try to shift to "P2P mode" at intervals