When using tokbox, how does one decrease the video stream resolution while keeping the video dimensions the same, in order to avoid hogging the CPU?
specify a lower resolution as described in the API and use CSS on the video element to specify the width/height so the dimensions do not automatically adapt to the resolution of the video stream.
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The datasheet of the OV2640 camera mentions the possibility to mirror or flip the image (see "REG04"). For my application it is, however, crucial to know the location of each pixel. Since the camera also crops the 1632x1232 sensor to a smaller, e.g., 1600x1200 image, the order of operations is important.
So does the camera first crop the image to the 1600x1200 window and mirror/flip it afterwards, or does the mirror/flip happen before the windowing?
I am using SDK 2.3 and develop an Android application with AS-15 and 20 camera that is exclusively dealing with liveview.
I unable to obtain from Liveview a higher resolution than 640x360px, while the camera specs mention a 1920×1080/30P (HQ).
How can I get the full resolution?
Is this a limitation of the API ? Why?
I've found that some (other) cameras implement get/setLiveviewSize and with the L it says
XGA size scale (the size varies depending on the camera models, and some camera models change the liveview quality instead of making the size larger.)
What are the models with the highest liveview resolution?
http://9gag.com/gif used to show the animations as gifs, now they are html5 videos. What is the reasoning behind such a decision?
The reason is simply that video compresses better than gif in many cases, particular when the gif is of some size or length.
Additionally, video can be streamed affecting traffic and when the displaying can start (almost right away), gifs has to be loaded completely before they can be shown (ore they will be shown slowly and progressive).
Now that most browsers are able to show video natively, video becomes a viable and desired option to animated gifs.
I am using HTML5 Canvas for rendering video, but the rendering is taking huge amount of CPU? I am using GtkLauncher (with webkit 1.8.0) for rendering the video on the Canvas.
Can some one please throw some light on this? Is video rendering on Canvas not efficient for embedded systems?
Also I would like to know, whether there is a way in HTML5 video tag to know the video frame rate, before I actually start to render the data on the Canvas. This I would need to know because I would have to set the timer (used for drawing the video frames) at that same frame rate .
Thanks and Regards,
Souvik
Most likely the video rendering is not accelerated and needs to
Decode on software
Resize on software
You did not give system details so this is just a guess. By poking browser internals you can dig out the truth.
Video framerate cannot be known beforehand and in theory can vary within one source. However if you host file yourself you can pre-extract this information using tools like ffmpeg and transfer the number in side-band (e.g. using AJAX / JSON).
I am writing a simple video messenger-like application, and therefore i need to get frames of some compromise size to be able to fit into the available bandwidth, and still to have the captured image not distorted.
To retrieve frames I am using QTCaptureVideoPreviewOutput class, and i am successfully getting frames in the didOutputVideoFrame callback. (i need raw frames - mostly because i am using a custom encoder, so i just would like to get "raw bitmaps").
The problem is that for these new iSight cameras i am getting literally huge frames.
Luckily, these classes for capturing raw frames (QTCaptureVideoPreviewOutput) provide method setPixelBufferAttributes that allows to specify what kind of frames would i like to get. If i am lucky enough to guess some frame size that camera supports, i can specify it and QTKit will switch the camera into this specified mode. If i am unlucky - i get a blurred image (because it was stretched/shrinked), and, most likely, non-proportional.
I have been searching trough lists.apple.com, and stackoverflow.com, the answer is "Apple currently does not provide functionality to retrieve camera's native frame sizes". Well, nothing i can do about that.
Maybe i should provide in settings the most common frame sizes, and the user has to try them to see what works for him? But what are these common frame sizes? Where could i get a list of the frame dimensions that UVC cameras generate usually?
For testing my application i am using a UVC compliant camera, but not an iSight. I assume not every user is using iSight either, and i am sure even between different models iSight cameras have different frame dimensions.
Or, maybe, i should switch the camera to the default mode, generate a few frames, see what sizes it generates, and at least i will have some proportions? This looks like a real hack, and doesn't seem to be natural. And the image is most likely going to be blurred again.
Could you please help me, how have your dealt with this issue? I am sure i am not the first one who is faced with it. What would be the approach you would choose?
Thank you,
James
You are right, iSight camera produces huge frames. However, I doubt you can switch the camera to a different mode by setting pixel buffer attributes. More likely you set the mode of processing the frames in the QTCaptureVideoPreviewOutput. Take a look at QTCaptureDecompressedVideoOutput if you have not done it yet.
We also use the sample buffer to get the frame size. So, I would not say it's a hack.
A more natural way would be to make your own Quicktime Component that implements your custom encoding algorithm. In this case Quicktime would be able to use inside QTCaptureMovieFileOutput during the capture session. It would be a proper, but also a hard way.