.._videoWriteHighGui:Creating a video with OpenCV****************************Goal====Whenever you work with video feeds you may eventually want to save your image processing result in a form of a new video file. For simple video outputs you can use the OpenCV built-in :huivideo:`VideoWriter <videowriter-videowriter>` class, designed for this. ..container:: enumeratevisibleitemswithsquare+ How to create a video file with OpenCV+ What type of video files you can create with OpenCV+ How to extract a given color channel from a videoAs a simple demonstration I'll just extract one of the RGB color channels of an input video file into a new video. You can control the flow of the application from its console line arguments:..container:: enumeratevisibleitemswithsquare+ The first argument points to the video file to work on+ The second argument may be one of the characters: R G B. This will specify which of the channels to extract.+ The last argument is the character Y (Yes) or N (No). If this is no, the codec used for the input video file will be the same as for the output. Otherwise, a window will pop up and allow you to select yourself the codec to use.For example, a valid command line would look like:..code-block::bash
video-write.exe video/Megamind.avi R Y
The source code===============You may also find the source code and these video file in the :file:`samples/cpp/tutorial_code/highgui/video-write/` folder of the OpenCV source library or :download:`download it from here <../../../../samples/cpp/tutorial_code/HighGUI/video-write/video-write.cpp>`...literalinclude:: ../../../../samples/cpp/tutorial_code/HighGUI/video-write/video-write.cpp:language:cpp:linenos::tab-width:4:lines:1-8, 21-22, 24-97The structure of a video========================For start, you should have an idea of just how a video file looks. Every video file in itself is a container. The type of the container is expressed in the files extension (for example *avi*, *mov* or *mkv*). This contains multiple elements like: video feeds, audio feeds or other tracks (like for example subtitles). How these feeds are stored is determined by the codec used for each one of them. In case of the audio tracks commonly used codecs are *mp3* or *aac*. For the video files the list is somehow longer and includes names such as *XVID*, *DIVX*, *H264* or *LAGS* (*Lagarith Lossless Codec*). The full list of codecs you may use on a system depends on just what one you have installed. ..image:: images/videoFileStructure.png:alt:The Structure of the video:align:centerAs you can see things can get really complicated with videos. However, OpenCV is mainly a computer vision library, not a video stream, codec and write one. Therefore, the developers tried to keep this part as simple as possible. Due to this OpenCV for video containers supports only the *avi* extension, its first version. A direct limitation of this is that you cannot save a video file larger than 2 GB. Furthermore you can only create and expand a single video track inside the container. No audio or other track editing support here. Nevertheless, any video codec present on your system might work. If you encounter some of these limitations you will need to look into more specialized video writing libraries such as *FFMpeg* or codecs as *HuffYUV*, *CorePNG* and *LCL*. As an alternative, create the video track with OpenCV and expand it with sound tracks or convert it to other formats by using video manipulation programs such as *VirtualDub* or *AviSynth*.The *VideoWriter* class=======================The content written here builds on the assumption you already read the :ref:`videoInputPSNRMSSIM` tutorial and you know how to read video files.To create a video file you just need to create an instance of the :huivideo:`VideoWriter <videowriter-videowriter>` class. You can specify its properties either via parameters in the constructor or later on via the :huivideo:`open <videowriter-open>` function. Either way, the parameters
