Does Kurento transcodes video automatically?

[ankit...@gmail.com]

Hi,

I just noticed that my chrome Android and Safari IOS cannot connect with each other without kurento in p2p. While with kurento it works, does kurento transcodes the video on the fly from vp8 to h264 or vice versa? I am getting very poor performance on my kurento, 150 users max on my 8GB and 4vcpu Digital ocean server while others claim 1000 users with 20%(jitsi) but I don't want to use them coz of one recording at a time. I want to disable this if it really happens, how can I do this? Will creating an Android app for chrome be better than transcoding for scalability.

Regards

[Micael Gallego]

Hi,

Kurento does transcoding if needed. In your case, if you want to avoid transcoding between chrome and ios you should force H264 codec between them. This can be done modifying SDP response like described in this post:

https://stackoverflow.com/questions/28984229/how-to-use-kurento-media-server-for-audio-only-stream

Also, if you want to be sure if transcoding is happening in KMS is looking to MediaTranscodingStateChange

https://doc-kurento.readthedocs.io/en/stable/features/events.html#mediatranscodingstatechange

Regarding to scalability, the only way to know most performant server is making performance testing yourself comparing different media servers. 

Regards.

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[euler27183]

Is it always the case that if both endpoints use H.264, then no video transcoding happens? What about if it is done across protocols like RTSP to WebRTC?

[Micael Gallego]

If both endpoints use the same H264 profile, then there is no transcoding at all. But it is possible that a IP cam only offer an incompatible H264 profile, then it is necessary to transcode to WebRTC. For that reason, the event it is very interesting.

Best regards

Micael Gallego

Kurento / OpenVidu Project Lead

On Mon, Apr 2, 2018 at 3:55 AM, euler27183 <volati...@gmail.com> wrote:

Is it always the case that if both endpoints use H.264, then no video transcoding happens? What about if it is done across protocols like RTSP to WebRTC?

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[Micael Gallego]

You can check if transcoding is happening querying this method:

https://doc-kurento.readthedocs.io/en/latest/_static/client-javadoc/org/kurento/client/MediaElement.html#isMediaTranscoding-org.kurento.client.MediaType-java.lang.String-

You can also subscribe to events.

In your case, you have to call to this method in the WebRtcEndpoint.

Best regards

Micael Gallego

Kurento / OpenVidu Project Lead

On Sun, Apr 1, 2018 at 10:27 PM, euler27183 <volati...@gmail.com> wrote:

Hi Micael,

Is there documentation as to whether Kurento video transcodes if you have a PlayerEndpoint using RTSP and send it to a WebRTC endpoint? If both endpoints use H.264, then does transcoding still happen? Does adapting bit rate on the WebRTC endpoint affect this?

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[Neil Young]

I have a WebRTC upstream delivering VP8 towards KMS. This is connected to an RTPEndpoint. AFAIK RTPEndpoint is just supporting H.264. Hence I'm pretty sure, that there is some transcoding happening. But I can't figure it out. From the system load on the KMS I see, that there must be a transcoding, because if I disable VP8 my WebRTC upstream is H.264 and the load is slightly lower.

I already tested to examine the both elements I have in my node server:

gWebRTCEndpoint.isMediaTranscoding("VIDEO").then((result) => { console.log("transcoding", result)})

gRtpEndpoint.isMediaTranscoding("VIDEO").then((result) => { console.log("transcoding", result) })

But both promises return false in all scenarios.

What am I doing wrong?

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[Paulo Lanzarin]

Although I believe the API state should be returning `true` if the media stream is being transcoded, you can

be completely sure about what's going on regarding transcoding state by skimming through the logs.

I believe setting `agnosticbin:5` should expose caps intersection data (you'd be able to see source and sink codecs).
`Kurento*:5,kms*:5` (sorry; can't remember the specific elements) should also enable log messages which clarifies

whether something is being transcoded. grep for `TRANSCODING ACTIVE` (`TRANSCODING INACTIVE` for the negation) in the logs.

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[Neil Young]

@prlanzarin You are completely right. I already recalled the required settings to observe this behaviour in the KMS and indeed, the transcoding happens.