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  1. #1
    Regular Contributor
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    Symbian^3 3gplibrary

    Hi all,

    i'm interested in the 3gplibrary usage.
    I have to extract frames from a video file (in 3gp or mp4 format) and save these images to file system and this lib seems to be helpful for me.
    In specific i would use the ReadVideoFrame(TDes8& aBuffer, TBool& aKeyFrame, TUint& aTimeStampInMs,TUint& aTimeStampInTimescale) function of this lib but i have a question:

    the first parameter of this function is the descriptor to store the video frames but the frames that are saved to this buffer are already decoded and represent an image that can be saved on file system or are coded data that have to be passed to the decoder?
    If the frames are already dedoded data how can i create a jpg image from the buffer content?

    Best regards

  2. #2
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    Re: Symbian^3 3gplibrary

    Supposing that the buffer contains coded data, exists a funtion to decode this data into a jpg file?

    Best Regards

  3. #3
    Nokia Developer Moderator
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    Re: Symbian^3 3gplibrary

    That TDes8 is most probably a complete uncompressed video frame. You can put it into a CFbsBitmap (its DataAddress and Lock/UnlockHeap methods can help), then save into a JPEG file using CImageEncoder.
    Note that there are good chances for that the video frame is in YUV or some other 'video' format, what you will have to convert to RGB in order to handle it correctly with CFbsBitmap.
    Check your API if it gives you further information about the size and actual format of that frame.

  4. #4
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    Re: Symbian^3 3gplibrary

    Thank you wizard_hu_,

    can you please show me how to put the TDes8 into a CFbsBitmap.

    Regards

  5. #5
    Nokia Developer Moderator
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    Re: Symbian^3 3gplibrary

    You need the resolution and data layout first. A TDes8 is just an array of bytes. In the simplest case you have a planar YUV frame, and a Mem::Copy into an EGray256 bitmap already provides the grayscale image. However you still need the resolution.

  6. #6
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    Re: Symbian^3 3gplibrary

    Hi wizard_hu_ and thank you so much for all the info that you gave me...

    i'm checking the function exported by the 3gplibrary and in specific of the C3GPParse class but i can't find a method that gives me the format of the extracted frame. I know the size of the frame but if i don't know the exact "video format" so i'm not able to correctly fill the BitMap.
    Where i can find this information?
    I have tried to post on the Symbian developer forum but i haven't received any answer.

    Best regards

  7. #7
    Nokia Developer Moderator
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    Re: Symbian^3 3gplibrary

    Checking the API suggest that these frames are not those frames what you expect. They are units of the video stream (which is also called 'frame'), and not decoded images. That is why you can get information about dependencies for example (decoding a single image often requires access to multiple other images).

  8. #8
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    Re: Symbian^3 3gplibrary

    ok,

    and there is no way to pass these "frames" to a video decoder who can decode them?

    Regards

  9. #9
    Nokia Developer Moderator
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    Re: Symbian^3 3gplibrary

    Such decoder API certainly exists somewhere, but I do not know the details.

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