OpenMediaLib User and Development Guide

• OpenMediaLib User Development Guide
  • Introduction
    • Terminology
  • High Level Use
  • Reverse Polish Notation
  • Applying RPN to Video/Audio
  • Clip Modifications
  • Compositing
  • Playlists
  • Stack Manipulations
  • Advanced Stack Usage
  • Aspect Ratio Considerations
  • The Encoding Filter Graph
  • Compositing Revisited
  • Really, Really Advanced Stack Usage
  • General Audio Issues
    • The Sample Calculator
    • Audio Resampling
    • Audio Mixing
  • Python
    • Python Callbacks and Filter Implementations
  • Interpolation
  • Threading

• Putting it All Together

• Appendices
  • Appendix A Input Operations
  • Appendix B Filter Operations
  • Appendix C Stores

The Sample Calculator

Although this is typically an issue for the plugin implementations to deal with, the cycle logic is exposed for general use (both in C++ and python).

There are two functions available – the first of which simply returns the number of required samples for a given frame offset and provided combination of frequency and frame rate and is prototyped in C++ as:

int audio_samples_for_frame( int frame, int frequency, int fps_num, int fps_den )

A sibling function is also provided which returns the number of samples which should have proceeded the requested frame position:

long long audio_samples_to_frame( int frame, int frequency, int fps_num, int fps_den )

And a final utility is provided to assist in the 'reseating' associated to frame rate interpolation:

audio_reseat_ptr create_audio_reseat( )

which returns a class with the following public interface:

	bool append( audio_type_ptr )
	audio_type_ptr retrieve( int samples, bool pad = false )
	void clear( )
	bool has( int )

Note that this doesn't provide resampling functionality – its role is simply to allow conversion from one frame rate to another by 'reseating' the audio samples according to the number of samples requested in the retrieve method.