I am able to extract samples out of a video using the readSample method. Now how can I play the data present in those samples? Or how to play IMFSample ?
Sample IMFSample is a block of data, such as video frame or a chunk of audio sequence. This is a tiny piece of data to be played alone. The API addresses more sophisticated playback scenarios, such as where playback is a session where one or more streams are streamed in sync.
Be sure to check Getting Started with MFPlay on MSDN to see how playback is set up with Media Foundation.
Related
I was recently playing a video on YouTube, and a thought came to my mind. As videos are played, a user can skip ahead in the video and the video just resumes at that point without any trouble.
What I can't seem to find is how this works, I know that when I request a file through HTTP it downloads the entire thing, so starting a binary stream halfway through the video doesn't seem possible using HTTP. Is there any RFC or related document on how browsers do this?
Thank you
There are a couple of different technologies but they all essentially allow you specific an offset in the video and then download a 'chunk' from there.
The simple way to do this is with byte ranges and HTTP progressive download 0 there is an RFC which covers this:
https://www.rfc-editor.org/rfc/rfc7233
A similar but slightly more complex mechanism is behind the various adaptive bit rate protocols, such as HLS, MPEG-DASH, Smooth-streaming etc. These protocols break a video into multiple chunks (e..g 10 second long segments) and also create several different encoding of the video each at different bit rates.
The client can then request the next chunk based on current network conditions - if the network is busy or if the client is using a low band witch connection it can request the next chunk from a low bit rate encoding of the video. If network connectivity improves then it can request from progressively higher bit rates until it reaches the maximum.
You can see this in action if you look at the 'stats for nerds' available in YouTube if you right click on the video - look at the connection speed graph.
This mechanism also means the client can request chunks from further ahead (or behind) than the current position in the video - so long as it is not live obviously!
It also allows faster start up if you do jump ahead as the playback can start from a lower bit rate which is faster to download and work up to the higher bit rate again. You can often see this when playing around with services like Netflix - if you jump ahead it may be lower quality for a little time initially.
YouTube stores the videos in several chunks. Once each chunk completes its download, you can play that chunk of video. Think of them as individual split videos.
When you try to jump into the middle, they will start downloading the necessary chunk of video and start playing. Therefore, you can jump to the middle.
I was using a callback mechanism to grab the webcam frames in my media application. It worked, but was slow due to certain additional buffer functions that were performed within the callback itself.
Now I am trying the other way to get frames. That is, call a method and grab the frame (instead of callback). I used a sample in CodeProject which makes use of IVMRWindowlessControl9::GetCurrentImage.
I encountered the following issues.
In a Microsoft webcam, the Preview didn't render (only black screen) on Windows 7. But the same camera rendered Preview on XP.
Here my doubt is, will the VMR specific functionalities be dependent on camera drivers on different platforms? Otherwise, how could this difference happen?
Wherever the sample application worked, I observed that the biBitCount member of the resulting BITMAPINFOHEADER structure is 32.
Is this a value set by application or a driver setting for VMR operations? How is this configured?
Finally, which is the best method to grab the webcam frames? A callback approach? Or a Direct approach?
Thanks in advance,
IVMRWindowlessControl9::GetCurrentImage is intended for occasional snapshots, not for regular image grabbing.
Quote from MSDN:
This method can be called at any time, no matter what state the filter
is in, whether running, stopped or paused. However, frequent calls to
this method will degrade video playback performance.
This methods reads back from video memory which is slow in first place. This methods does conversion (that is, slow again) to RGB color space because this format is most suitable for for non-streaming apps and gives less compatibility issues.
All in all, you can use it for periodic image grabbing, however this is not what you are supposed to do. To capture at streaming rate you need you use a filter in the pipeline, or Sample Grabber with callback.
I'm using two custom push filters to inject audio and video (uncompressed RGB) into a DirectShow graph. I'm making a video capture application, so I'd like to encode the frames as they come in and store them in a file.
Up until now, I've used the ASF Writer to encode the input to a WMV file, but it appears the renderer is too slow to process high resolution input (such as 1920x1200x32). At least, FillBuffer() seems to only be able to process around 6-15 FPS, which obviously isn't fast enough.
I've tried increasing the cBuffers count in DecideBufferSize(), but that only pushes the problem to a later point, of course.
What are my options to speed up the process? What's the right way to do live high res encoding via DirectShow? I eventually want to end up with a WMV video, but maybe that has to be a post-processing step.
You have great answers posted here to your question: High resolution capture and encoding too slow. The task is too complex for the CPU in your system, which is just not fast enough to perform realtime video encoding in the configuration you set it to work.
What exactly does the scan media features values progressive and interlace do exactly in simple terms? And are these the only values available for the scan feature?
They have to do with the output method of the screen of the device.
Describes the scanning process of television output devices.
Source.
progressive and interlace are the only two possible values.
Progressive Scan
Progressive (or noninterlaced scanning) is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence.
Source.
Interlaced Scan
Interlaced video is a technique of doubling the perceived frame rate of a video signal without consuming extra bandwidth. Since the interlaced signal contains the two fields of a video frame shot at two different times, it enhances motion perception to the viewer and reduces flicker by taking advantage of the persistence of vision effect.
Source.
It is used in style sheets for television. More info (book excerpt) here. If Interlaced and progressive videos interest you in some way, you can read about it here.
I am working on a Flex application/game where a lot of UIComponents are moved around on a canvas.
I would like to "record" an flv movie of the movement on the canvas. Is there anyway this can be accomplished ?
I essentially want my users to be able to record small flv videos of their games to be uploaded on youtube.
Any ideas or suggestions about how to do this ?
There is SimpleFlvWriter (for AIR). You may modify it to get a non-AIR version. But memory management will be an issue since BitmapData will take up a lot of memory... It may be possible for a few seconds flv but definite not for several minutes.
Usually we stream things to a Flash server (eg. Flash Media Server, Red5) and let the server create the flv. But you need to find a way to convert the screen captures to NetStream. Or you may find other server side technology that can create flv from sequence of BitmapData. But in anyway it will consume a lot of bandwidth.
An alternative I can think of, is to save all the game commands(in XML, or other text format) and send it to the server. And you write a program in server-side to generate the flv from only the game commands. But it will be the most difficult solution to be implemented.