VideoRecorder Class Reference

Records video and audio output to a file. More...

#include <jngl/record/VideoRecorder.hpp>

Public Member Functions
	VideoRecorder (std::string_view filename, bool lossless=false)
	Creates a new video recorder that writes to the specified file (saved in your data/ directory).
	~VideoRecorder () override
	Finalizes and closes the video file.
	VideoRecorder (const VideoRecorder &)=delete
VideoRecorder &	operator= (const VideoRecorder &)=delete
	VideoRecorder (VideoRecorder &&)=delete
VideoRecorder &	operator= (VideoRecorder &&)=delete
void	fillAudioBuffer (std::unique_ptr< float[]> samples)
	Assumes 44.1 kHz, stereo audio input and getting called exactly getStepsPerSecond() times per second.
void	step () override
	Advance the game logic.
void	draw () const override
	Draw the game state.
Public Member Functions inherited from Job
virtual void	onFileDrop (const std::filesystem::path &)
	Called when a file has been dropped onto the window.
virtual void	onControllersChanged ()
	Whenever the return value of jngl::getConnectedControllers would change, this method gets called.
	Job ()=default
	Does nothing.
	Job (const Job &)=default
	Copy constructor.
Job &	operator= (const Job &)=default
	Copy assignment.
	Job (Job &&)=default
	Move constructor.
Job &	operator= (Job &&)=default
	Move assignment.
virtual	~Job ()
	Does nothing.

Detailed Description

Records video and audio output to a file.

VideoRecorder is a background job that captures the rendered frames and audio samples to create a video file.

The recorder captures:

• Video: Frames are captured at the current window resolution and frame rate (jngl::getStepsPerSecond())
• Audio: Stereo audio at 44.1 kHz sample rate

Note

Recording requires JNGL to be compiled with JNGL_RECORD enabled and FFmpeg libraries available. Pass -DJNGL_RECORD=1 to CMake during configuration. On macOS, install FFmpeg with brew install ffmpeg.

Example usage:

#include <jngl.hpp>
#include <jngl/init.hpp>
#include <jngl/record/VideoRecorder.hpp>
 
jngl::AppParameters jnglInit() {
    jngl::AppParameters params;
    params.start = []() {
        // Start recording to output.mkv
        jngl::addJob<jngl::VideoRecorder>("output.mkv");
        // Your scene setup here...
    };
    return params;
}

The VideoRecorder will automatically capture frames and audio as your application runs. Remove the job or let it go out of scope to finalize and close the video file.

Warning

During recording, the game will run at a slower wall-clock speed to ensure no frames are dropped. The video encoding is synchronous and the application waits for each frame to be encoded before proceeding. This means the game runs slower in real-time but produces a smooth video at the target frame rate. Audio playback is muted during recording since the game is not running at normal speed.

The video container is chosen based on the file extension you provide. For example:

• .mkv: Matroska container
• .mp4: MP4 container

By default, lossy codecs are used (H.264 for video, AAC for audio) to produce reasonably sized files. If you want lossless quality, pass true for the lossless parameter when creating the VideoRecorder.

If you chose to use lossless, you would probably convert the resulting .mkv file to a compressed format later so you can upload it to Google Play or the Apple App Store. Use ffmpeg on the command line for that:

ffmpeg -i foo.mkv \
       -c:v libx264 \
       -profile:v high \
       -level 4.2 \
       -pix_fmt yuv420p \
       -r 30 \
       -c:a aac \
       -b:a 160k \
       -movflags +faststart \
       output.mp4

This command converts foo.mkv to output.mp4 using H.264 video codec and AAC audio codec.

Definition at line 78 of file VideoRecorder.hpp.

Inheritance diagram for VideoRecorder:

Collaboration diagram for VideoRecorder:

Constructor & Destructor Documentation

VideoRecorder()

VideoRecorder ( std::string_view filename, bool lossless = false )

explicit

Creates a new video recorder that writes to the specified file (saved in your data/ directory).

Initializes video and audio encoding with the following common settings:

• Frame rate: Current application frame rate (jngl::getStepsPerSecond())
• Resolution: Current window dimensions (jngl::getWindowWidth() x jngl::getWindowHeight())

Parameters

filename	Path to the output video file. Use appropriate file extension (e.g., .mkv, .mp4) to select the container format.
lossless	If true, uses lossless codecs (FFV1 for video, FLAC for audio). If false, uses lossy codecs (H.264 for video, AAC for audio). Default is false.

Exceptions

std::runtime_error

if video encoding setup fails (e.g., codecs not found, file cannot be opened)

~VideoRecorder()

~VideoRecorder ( )

override

Finalizes and closes the video file.

Flushes any remaining frames and audio data, writes the container trailer, and releases all encoding resources.

Member Function Documentation

step()

void step ( )

overridevirtual

Advance the game logic.

This function gets called 60 times per second or whatever has been set by setStepsPerSecond().

Note

JNGL's main loop calls all Jobs' step() functions before the active Scene's step()

Implements Job.

draw()

void draw ( ) const

overridevirtual

Draw the game state.

As it isn't garuanteed that this function is called as often as Job::step, you shouldn't change any game state in it.

Note

JNGL's main loop calls all Jobs' draw() functions after the active Scene's draw()

Implements Job.

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The documentation for this class was generated from the following file:

• jngl/record/VideoRecorder.hpp