C++ buffer with Qt

Question

I made a videoplayer with Qt, OpenGl and FFMpeg which works quite well.

Now I want to use multi-threading and a buffer to have better performances. I've set up a thread which decode the frames and store it in a QMap :

QMap<int, uint8_t *> myBuffer;

The first int being the timecode and the second point to the OpenGl Texture.

Everytime I decode a frame, I add it to the buffer using new and as soon as the frame is read, I delete it.

Is assume this is not the best way to do it, not in term of memory management (no memory leak) but in term of performance.

Is there a better approach to do this ?

Answer 1

You could decode directly into OpenGL pixel buffer objects. Create a number (3 or 4 should suffice) PBOs and have the renderer thread mapped at least 2 of them into process address space using glMapBuffer and queue the location and PBO ID into a pool of available buffers. To decode a frame, dequeue the pointer/ID from the available PBO pool and decode into the provided memory. Once a frame has been decoded, queue the ID of the used PBO into a "decoded" pool, which the renderer thread uses to unmap with glUnmapBuffer(); immediately followed by a load into texture using glTexSubImage2D; the texture upload happens asynchronously. Enqueue the texture ID into a "ready to display" queue/FIFO. Then have the renderer dequeue from the "ready to display" the next to display texture; by keeping at least 3 elements in the "ready to display" FIFO frames get asynchronously uploaded while drawing the previously decoded frames without OpenGL blocking because it has to wait for previous steps to complete.