CODEWITHSUNDEEP
htmlvideostreamingvideo-streamingdelay
Alvin
Alvin

Reputation: 31

HLS - how to reduce delay?

Anyone know how configure the HLS media server for reduce a little bit the delay of live streaming video?
what types of parameters i need to change?
I had heard that you could do some tuning using parameters like this: HLSMediaFileDuration

Thanks in advance

Upvotes: 1

Views: 19630

Answers (4)

jjramos
jjramos

Reputation: 2094

I was having the same problem and the keys for me were:

  1. Lower the segment length. I set it to 2s because I'm streaming on a local network. In other type of networks, you need to be careful with the overhead that a low segment length adds that can impact your playback quality.
  2. In your manifest, make sure the #EXT-X-TARGETDURATION is accurate. From here:

The EXT-X-TARGETDURATION tag specifies the maximum Media Segment duration. The EXTINF duration of each Media Segment in the Playlist file, when rounded to the nearest integer, MUST be less than or equal to the target duration; longer segments can trigger playback stalls or other errors. It applies to the entire Playlist file.

For some reason, the #EXT-X-TARGETDURATION in my manifest was set to 5 and I was seeing a 16-20s delay. After changing that value to 2, which is the correct one according to my segments' length, I am now seeing delays of 6-10s.

In summary, you should expect a delay of at least 3X your #EXT-X-TARGETDURATION. So, lowering the segment length and the #EXT-X-TARGETDURATION value should help reducing the delay.

Upvotes: 1

themoah
themoah

Reputation: 187

Actually, Apple recommend to divide your file to small chunks this equal length of file, integers.

In practice, there is huge difference between players. Some of them parse manifest changing this values.

Known practice is to pre-cache in memory first chunks in low & medium resolution (Or try to download them in background of app/page - Amazon does this, though their video is MSS)

Upvotes: 0

Grant
Grant

Reputation: 1648

A Http Live Streaming system typically has an encoder which produces segments of a certain number of seconds and a media server (web server) which serves playlists containing a list of URLs to these segments to player applications.

Media Files = Segments = .ts files = MPEG2-TS files (in HLS speak)

There are some ways to reduce the delay in HLS:

  1. Reduce the encoded segment length from Apple's recommended 10 seconds to 5 seconds or less. Reducing segment length increases network overhead and load on the web server.
  2. Use lower bitrates, larger .ts files take longer to upload and download. If you use multi-bitrate streams, make sure the first bitrate listed in the playlist is a little lower than the bitrate most of your users use. This will reduce the time to start playing back the stream
  3. Get the segments from the encoder to the web server faster. Upload while still encoding if possible. Update the playlist as soon as the segment has finished uploading

Also remember that the higher the delay the better the quality of your stream (low delay = lower quality). With larger segments, there is less overhead so more space for video data. Taking a longer time to encode results in better quality. More buffering results in less chance of video streams stuttering on playback. HLS is all about trading quality of playback for longer delay, so you will never be able to use HLS for things like video conferencing. Typical delay in HLS is 30-60 sec, minimum in practice is around 15 sec. If you want low delay use RTP for streaming, but good luck getting good quality on low or variable speed networks.

Upvotes: 10

Yury
Yury

Reputation: 691

Please specify which media server you use. Generally speaking, yes - changing chunk size will definitely affect delay time. The less is the first chunk, the quicker the video will be shown in the player.

Upvotes: 0

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