136 lines
6.0 KiB
Markdown
136 lines
6.0 KiB
Markdown
---
|
|
slug: why-dash-is-bad-solution-for-live-streaming
|
|
title: SRS - Why DASH Is Bad Solution for Live Streaming
|
|
authors: []
|
|
tags: [video, dash, live, streaming]
|
|
custom_edit_url: null
|
|
---
|
|
|
|
# Why DASH Is Bad Solution for Live Streaming
|
|
|
|
> Written by [John](https://github.com/xiaozhihong), [Winlin](https://github.com/winlinvip)
|
|
|
|
What is MPEG-DASH(Dynamic Adaptive Streaming over HTTP)? Because Apple HLS is not good enough, so some guys wanted to
|
|
fix it and created an even worse protocol, named DASH or MPEG-DASH.
|
|
|
|
Well, it's just a joke for any new technology, especially when it's new and there are some issues. However, it's really
|
|
true for DASH today, at 2022.11, because we're really suffering while maintaining it.
|
|
|
|
But, DASH is becoming more and more popular protocol for live streaming, and we believe that all issues will be fixed
|
|
in not very far future, so let's take a look about these issues.
|
|
|
|
<!--truncate-->
|
|
|
|
## Good News: Normal Scenario
|
|
|
|
DASH is available for both VoD and LIVE streaming, and it works for `NORMAL` use scenarios. Let's have a glance.
|
|
|
|
```bash
|
|
docker run --rm -it -p 8080:8080 -p 1935:1935 \
|
|
-e SRS_HTTP_SERVER_ENABLED=on -e SRS_VHOST_DASH_ENABLED=on \
|
|
ossrs/srs:5
|
|
```
|
|
|
|
Publish a live stream by RTMP to media server:
|
|
|
|
```bash
|
|
docker run --rm -it ossrs/srs:encoder ffmpeg -stream_loop -1 -re -i doc/source.flv \
|
|
-c copy -f flv rtmp://host.docker.internal/live/livestream
|
|
```
|
|
|
|
Finally you're able to play DASH by:
|
|
|
|
* VLC: `http://localhost:8080/live/livestream.mpd`
|
|
* FFmpeg: `ffplay http://localhost:8080/live/livestream.mpd`
|
|
* H5 [srs-player](http://localhost:8080/players/srs_player.html?stream=livestream.mpd&autostart=true)
|
|
|
|
It's very easy, right?!
|
|
|
|
## Bad News: Republishing
|
|
|
|
What's the issues of DASH?
|
|
|
|
If you open [srs-player](http://localhost:8080/players/srs_player.html?stream=livestream.mpd&autostart=true) and wait
|
|
for about serval minutes while stream is republished, you will find out that the player might be stuck.
|
|
|
|
Yep, it's maybe the problem of srs-player, which use [dash.js@v4.5.1](https://github.com/Dash-Industry-Forum/dash.js),
|
|
so let's choose another player.
|
|
|
|
What about VLC? Also fails when stream is republishing.
|
|
|
|
What about ffplay? Also fails.
|
|
|
|
All these issues are literally caused by republishing, that is, when you stop the stream, and then publish the stream,
|
|
players might be stuck.
|
|
|
|
> Note: Player will resume to play when refresh the page.
|
|
|
|
For HLS, the `EXT-X-DISCONTINUITY` is design for this situation, and all players work very well when stream republishing.
|
|
|
|
For DASH, the spec introduces a new Period, but it does work whatever. So SRS will regenerate a new MPD file, it makes
|
|
the dash.js happy, but doesn't work for VLC or ffplay.
|
|
|
|
## Bad News: MPD Mode
|
|
|
|
If use `SegmentTimeline` and use `$Time$` mode, there is bug for `VLC 3.0.17`, but `VLC 4.0` is ok. For more detail
|
|
information about this issue, please see [VLC#2845](https://code.videolan.org/videolan/vlc/-/merge_requests/2845).
|
|
|
|
If use `SegmentTemplate` without `SegmentTimeline`, player will guess the file name, but it literally fails while
|
|
streaming for a long time. SRS 4.0 uses this mode and there is some bugs about it, see [SRS#1864](https://github.com/ossrs/srs/issues/1864).
|
|
So SRS 5.0 fix this issue and use another mode.
|
|
|
|
SRS 5.0 use `SegmentTemplate` with `SegmentTimeline`, and use `$Number$` but not `$Time$` mode, because there is also
|
|
bug for `$Time$` mode for VLC as previous description.
|
|
|
|
Right now, at 2022.11, the best compatible mode is `SegmentTemplate` with `SegmentTimeline` and `$Number$` mode, which
|
|
is used for SRS 5.0. H5(dash.js) works well, but VLC/ffplay still have some issues.
|
|
|
|
## About HEVC
|
|
|
|
[Chrome 105+](https://caniuse.com/?search=HEVC) supports HEVC by default, see [this post](https://zhuanlan.zhihu.com/p/541082191).
|
|
|
|
You're able to play HEVC over mp4 directly by H5 video, or by MSE if HTTP-FLV/HTTP-TS/HLS etc. Please use [mpegts.js](https://github.com/xqq/mpegts.js)
|
|
to play HEVC over HTTP-FLV or HTTP-TS, see [SRS#465](https://github.com/ossrs/srs/issues/465#usage).
|
|
|
|
For DASH, the protocol does not limit to use H.264 or HEVC, because it use MP4 which can be play by MSE by Chrome 105+.
|
|
|
|
However, there still some extra work for media server, to support MP4 or DASH with HEVC. SRS 6.0 is still working on it,
|
|
for detail information please see [SRS#465](https://github.com/ossrs/srs/issues/465#status-of-hevc-in-srs).
|
|
|
|
## Publish by H5 then Delivery by DASH
|
|
|
|
If wants to publish live stream by H5, then delivery by MPEG-DASH, there is a solution:
|
|
|
|
```bash
|
|
Camera/Microphone --WebRTC---> SRS --DASH--> Viewers
|
|
```
|
|
|
|
Because the only way is to use WebRTC to access the camera and microphone for H5, so you must use WebRTC to ingest live
|
|
stream to media server such as SRS. Then SRS will covert WebRTC to RTMP, finally covert to MPEG-DASH, plese see [this post](../docs/v5/doc/getting-started#webrtc-for-live-streaming).
|
|
|
|
Note that SRS also support [WebRTC-HTTP ingestion protocol (WHIP)](https://datatracker.ietf.org/doc/draft-ietf-wish-whip/),
|
|
for example, [srs-unity](https://github.com/ossrs/srs-unity) uses WHIP to publish Unity camera stream.
|
|
|
|
## Cloud Service
|
|
|
|
At SRS, our goal is to establish a non-profit, open-source community dedicated to creating an all-in-one,
|
|
out-of-the-box, open-source video solution for live streaming and WebRTC online services.
|
|
|
|
Additionally, we offer a [Cloud](../cloud) service for those who prefer to use cloud service instead of building from
|
|
scratch. Our cloud service features global network acceleration, enhanced congestion control algorithms,
|
|
client SDKs for all platforms, and some free quota.
|
|
|
|
To learn more about our cloud service, click [here](../cloud).
|
|
|
|
## Conclusion
|
|
|
|
DASH is a relative new and good live streaming protocol. After about two years, SRS 5.0 has always been fixing bug and
|
|
now we think it's ready and stable to use DASH in your online product if you want.
|
|
|
|
## Contact
|
|
|
|
If you'd like to discuss with SRS, you are welcome to [discord](https://discord.gg/yZ4BnPmHAd)
|
|
|
|
|
|
|