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Greetings VideoLAN community,

My name is Benjamin Arnaud. I'm new on this board and looking forward to share interesting stuff with you.

I've been playing around a little bit with LibVLC RC 2.0 lately. Congratulation on switching to LGPL.

I'm using libvlc_video_set_callbacks and libvlc_video_set_format_callbacks inside a Qt QGraphicsScene.

I'm using the RV24 chroma setting and I'm rendering my frames using native Opengl with glTexSubImage2D.

It's working fine with a mp4 h264 file. I tried with a youtube webM video file, my frames turn black and white with a strange tearing. When switching to RV32, the rendering seems ok.

Is there an issue between RV24 and the WebM format ? Is there a performance difference between RV24 and RV32 on VLC side ?

Thanks guys.

B.A.

Greetings VideoLAN community,

My name is Benjamin Arnaud. I'm new on this board and looking forward to share interesting stuff with you.

I've been playing around a little bit with LibVLC RC 2.0 lately. Congratulation on switching to LGPL.

Thanks! And Welcome!

I'm using libvlc_video_set_callbacks and libvlc_video_set_format_callbacks inside a Qt QGraphicsScene.

I'm using the RV24 chroma setting and I'm rendering my frames using native Opengl with glTexSubImage2D.

It's working fine with a mp4 h264 file. I tried with a youtube webM video file, my frames turn black and white with a strange tearing. When switching to RV32, the rendering seems ok.

Is there an issue between RV24 and the WebM format ? Is there a performance difference between RV24 and RV32 on VLC side ?

You should look at the logs of VLC.

Thanks I'll take a look.

"--verbose=2" should do the trick.

Yes, it should

I don't see anything too shocking here. Am I missing something ?

What happens in the logs in the case of h264?

For mp4 / h264 I get the following:

It's working fine with a mp4 h264 file. I tried with a youtube webM video file, my frames turn black and white with a strange tearing. When switching to RV32, the rendering seems ok.

Is this a case of RGB vs. BGR? OpenGL expects BGR for 24bit rendering and VLC (if I remember correcty) supplies it as RGB. This doesn't explain the tearing however.

Well I had the BGR vs RGB issue with my opengl implementation.

This is not related since I have the same tearing and black and white result even when using a QImage + rgbswapped() function.

Is RV24 supposed to be faster than RV32 anyway ?

RV24 is faster from a glTexSubImage2D perspective since it is less data being pushed to the video card, however if the rgb is being swapped in software it might counter those gains.

RGB is going to be slow, no matter what kind of RGB.

Use YUV if you care about speed. There are no other options. And yes, that pretty much eliminates OpenGL, unless shaders are involved.

Thanks Remi.

So I can expect Opengl and YUV to RGB shaders to be significantly faster than VLC's own RGB conversion ?

Doesn't RV32 / RV24 already use Opengl shaders to perform that conversion on VLC 2.0 ?

B.A.

VLC's color spaces conversions are done on CPU. Relative speed depends on the relative speed and use of the CPU and the GPU.

I'll give YUV + Opengl a shot,

Judging from what I read here: http://wiki.videolan.org/YUV I should use UYVY for 24bit video, then perform the conversion on the GPU using a UYVY to RGB shader.

UPDATE: after further reading it seems YUV 4:2:0 I420 is the best option.

Also using glTexSubImage2D together with a pixel buffer object might increase texture upload performances: http://www.songho.ca/opengl/gl_pbo.html#unpack

the VLC OpenGL uses fragment shaders ARB to do such conversion.

Can you point to an example that uses this or some hints about how to use it?

Thanks!

Read the opengl output code.

I'll give YUV + Opengl a shot,

Judging from what I read here: http://wiki.videolan.org/YUV I should use UYVY for 24bit video, then perform the conversion on the GPU using a UYVY to RGB shader.

UPDATE: after further reading it seems YUV 4:2:0 I420 is the best option.

Also using glTexSubImage2D together with a pixel buffer object might increase texture upload performances: http://www.songho.ca/opengl/gl_pbo.html#unpack

Hello,

Any chance to show your example, for some reason it keeps crashing on Mac OS when i am trying to integrate this with QML scene. No worries if it is proprietary, i will keep digging.

Thanks

For the record, UYVY is 16-bits and U420 is 12-bits. Only I444 is 24-bits, but it is rarely used in video streams.

vseryakov,

First, take a look at the VLC source code for a proper OpenGL implementation:

vlc/modules/video_output/opengl.c

Then use a QGraphicsView together with a QGLWidget viewport.

Then use QPainter::beginNativePaint() in the paintEvent and render your frame.

You get best performances with VLC YUV decoding + multitexturing and a shader.

Also it's a good idea to run VLC from its own QThread communicating with QEvent(s).

B.A.