Consider 2 raster systems with resolution 640X480 and 1280X1024. How many pixels could be accessed per second in each of these systems by display controller that refreshes screen at rates of 60 frames per second. What is access time per pixel in each system?
Please explain in details
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I have been analyzing the JSON file generated using chrome://webrtc-internal, while running webrtc on 2 PCS.
I looked at Stats API to verify how webrtc-internal computes the keyframe rate.
By looking at Stats API/ RTC Remote Inbound RTP Video Stream, it contains keyFramesDecoded which represents the total number of key frames, such as key frames in VP8, given that I set the codec to VP8.
keyFramesDecoded values are very small, i.e., 2 for a couple of minutes, and similarly for 3 and ...
My question is: How does the graph here make sense for keyFramesDecoded?
That looks right to me.
Chrome is configured to send a keyframe every 3000 frames. That means for 30fps you will see a keyframe every 100 seconds. The framesDecoded is being construct by lots of delta frames.
If you are in a unconstrained network and not dealing with lots of change in your video I would expect to see graphs like yours.
I'm creating a Raspberry Pi Zero W security camera and am attempting to integrate motion detection using Node.js. Images are being taken with Pi camera module at 8 Megapixels (3280x2464 pixels, roughly 5MB per image).
On a Pi Zero, resources are limited, so loading an entire image from file to Node.js may limit how fast I can capture then evaluate large photographs. Surprisingly, I capture about two 8MB images per second in a background time lapse process and hope to continue to capture the largest sized images roughly once per second at least. One resource that could help with this is extracting the embedded thumbnail from the large image (thumbnail size customizable in raspistill application).
Do you have thoughts on how I could quickly extract the thumbnail from a large image without loading the full image in Node.js? So far I've found a partial answer here. I'm guessing I would manage this through a buffer somehow?
I want to built a SoundWave sampling an audio stream.
I read that a good method is to get amplitude of the audio stream and represent it with a Polygon. But, suppose we have and AudioGraph with just a DeviceInputNode and a FileOutpuNode (a simple recorder).
How can I get the amplitude from a node of the AudioGraph?
What is the best way to periodize this sampling? Is a DispatcherTimer good enough?
Any help will be appreciated.
First, everything you care about is kind of here:
uwp AudioGraph audio processing
But since you have a different starting point, I'll explain some more core things.
An AudioGraph node is already periodized for you -- it's generally how audio works. I think Win10 defaults to periods of 10ms and/or 20ms, but this can be set (theoretically) via the AudioGraphSettings.DesiredSamplesPerQuantum setting, with the AudioGraphSettings.QuantumSizeSelectionMode = QuantumSizeSelectionMode.ClosestToDesired; I believe the success of this functionality actually depends on your audio hardware and not the OS specifically. My PC can only do 480 and 960. This number is how many samples of the audio signal to accumulate per channel (mono is one channel, stereo is two channels, etc...), and this number will also set the callback timing as a by-product.
Win10 and most devices default to 48000Hz sample rate, which means they are measuring/output data that many times per second. So with my QuantumSize of 480 for every frame of audio, i am getting 48000/480 or 100 frames every second, which means i'm getting them every 10 milliseconds by default. If you set your quantum to 960 samples per frame, you would get 50 frames every second, or a frame every 20ms.
To get a callback into that frame of audio every quantum, you need to register an event into the AudioGraph.QuantumProcessed handler. You can directly reference the link above for how to do that.
So by default, a frame of data is stored in an array of 480 floats from [-1,+1]. And to get the amplitude, you just average the absolute value of this data.
This part, including handling multiple channels of audio, is explained more thoroughly in my other post.
Have fun!
Many of the embedded/mobile GPUs are providing access to performance registers called Pixel Write Speed and Texel Write speed. Could you explain how those terms can be interpreted and defined from the actual GPU hardware point of view?
I would assume the difference between pixel and texel is pretty clear for you. Anyway, just to make this answer a little bit more "universal":
A pixel is the fundamental unit of screen space.
A texel, or texture element (also texture pixel) is the fundamental unit of texture space.
Textures are represented by arrays of texels, just as pictures are
represented by arrays of pixels. When texturing a 3D surface (a
process known as texture mapping) the renderer maps texels to
appropriate pixels in the output picture.
BTW, it is more common to use fill rate instead of write speed and you can easily find all required information, since this terminology is quite old and widely-used.
Answering your question
All fill-rate numbers (whatever definition is used) are expressed in
Mpixels/sec or Mtexels/sec.
Well the original idea behind fill-rate was the number of finished
pixels written to the frame buffer. This fits with the definition of
Theoretical Peak fill-rate. So in the good old days it made sense to
express that number in Mpixels.
However with the second generation of 3D accelerators a new feature
was added. This feature allows you to render to an off screen surface
and to use that as a texture in the next frame. So the values written
to the buffer are not necessarily on screen pixels anymore, they might
be texels of a texture. This process allows several cool special
effects, imagine rendering a room, now you store this picture of a
room as a texture. Now you don't show this picture of the room but you
use the picture as a texture for a mirror or even a reflection map.
Another reason to use MTexels is that games are starting to use
several layers of multi-texture effects, this means that a on-screen
pixel is constructed from various sub-pixels that end up being blended
together to form the final pixel. So it makes more sense to express
the fill-rate in terms of these sub-results, and you could refer to
them as texels.
Read the whole article - Fill Rate Explained
Additional details can be found here - Texture Fill Rate
Update
Texture Fill Rate = (# of TMU - texture mapping unit) x (Core Clock)
The number of textured pixels the card can render to the
screen every second.
It is obvious that the card with more TMUs will be faster at processing texture information.
The performance registers/counters Pixel Write Speed and Texel Write speed maintain stats / count operations about pixel and texel processed/written. I will explain the peak (maximum possible) fill rates.
Pixel Rate
A picture element is a physical point in a raster image, smallest
element of display device screen.
Pixel rate is the maximum amount of pixels the GPU could possibly write to the local memory in one second, measured in millions of pixels per second. The actual pixel output rate also depends on quite a few other factors, most notably the memory bandwidth - the lower the memory bandwidth is, the lower the ability to get to the maximum fill rate.
The pixel rate is calculated by multiplying the number of ROPs (Raster Operations Pipelines - aka Render Output Units) by the the core clock speed.
Render Output Units : The pixel pipelines take pixel and texel information and process it, via specific matrix and vector operations, into a final pixel or depth value. The ROPs perform the transactions between the relevant buffers in the local memory.
Importance : Higher the pixel rate, higher is the screen resolution of the GPU.
Texel Rate
A texture element is the fundamental unit of texture space (a tile of
3D object surface).
Texel rate is the maximum number of texture map elements (texels) that can be processed per second. It is measured in millions of texels in one second
This is calculated by multiplying the total number of texture units by the core speed of the chip.
Texture Mapping Units : Textures need to be addressed and filtered. This job is done by TMUs that work in conjunction with pixel and vertex shader units. It is the TMU's job to apply texture operations to pixels.
Importance : Higher the texel rate, faster the game renders displays demanding games fluently.
Example : Not a nVidia fan but here are specs for GTX 680, (could not find much for embedded GPU)
Model Geforce GTX 680
Memory 2048 MB
Core Speed 1006 MHz
Shader Speed 1006 MHz
Memory Speed 1502 MHz (6008 MHz effective)
Unified Shaders 1536
Texture Mapping Units 128
Render Output Units 32
Bandwidth 192256 MB/sec
Texel Rate 128768 Mtexels/sec
Pixel Rate 32192 Mpixels/sec
I'm looking into rendering frames at a high rate (ideally next to the max monitor rate) and I was wondering if anyone had any idea at what level I should start looking into: kernel/driver level (OS space) ? X11 level ? svgalib (userspace) ?
On a modern computer, you can do it using the ordinary tools and APIs for graphics. If you have full frames full of random pixels, a simple bit blit from an in-memory buffer will perform more than adequately. Without any optimization work, I found that I could generate more than 500 frames per second on Windows XP using 2008 PCs.