lib/frameFilter.h

/*
 *  Copyright (C) 2020 Savoir-faire Linux Inc.
 *
 *  Author: Aline Gondim Santos <aline.gondimsantos@savoirfairelinux.com>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA.
 */

#ifndef FRAMEFILTER_H
#define FRAMEFILTER_H

#include <map>
#include <string>
#include <vector>
#include "mediaStream.h"
#include <memory>

extern "C" {
struct AVFilterContext;
struct AVFilterGraph;
struct AVFilterInOut;
}

namespace jami {

/**
 * @brief Provides access to libavfilter.
 *
 * Can be used for filters with unlimited number of inputs.
 * Multiple outputs are not supported. They add complexity for little gain.
 *
 * For information on how to write a filter graph description, see:
 * https://ffmpeg.org/ffmpeg-filters.html
 * http://trac.ffmpeg.org/wiki/FilteringGuide
 *
 * It is required to name each filter graph input. These names are used to feed the correct input.
 * It is the same name that will be passed as second argument to feedInput(AVFrame*, std::string).
 *
 * Examples:
 *
 * - "[in1] scale=320:240"
 * Scales the input to 320x240.
 *
 * - "[in1] scale=iw/4:ih/4 [mid]; [in2] [mid] overlay=main_w-overlay_w-10:main_h-overlay_h-10"
 * in1 will be scaled to 1/16th its size and placed over in2 in the bottom right corner. When
 * feeding frames to the filter, you need to specify whether the frame is destined for in1 or in2.
 */
class FrameFilter
{
public:
    FrameFilter();
    ~FrameFilter();

    /**
     * @brief Initializes the filter graph with one or more inputs and one output. Returns a
     * negative code on error.
     */
    int initialize(const std::string& filterDesc, std::vector<MediaStream> msps);

    /**
     * @brief Returns a MediaStream object describing the input specified by @inputName.
     */
    MediaStream getInputParams(const std::string& inputName) const;

    /**
     * @brief Returns a MediaStream struct describing the frames that will be output.
     *
     * When called in an invalid state, the returned format will be invalid (less than 0).
     */
    MediaStream getOutputParams() const;

    /**
     * @brief Give the specified source filter an input frame.
     *
     * Caller is responsible for freeing the frame.
     *
     * NOTE Will fail if @inputName is not found in the graph.
     */
    int feedInput(AVFrame* frame, const std::string& inputName);
    int feedEOF(const std::string& inputName);

    /**
     * @brief Pull a frame from the filter graph. Caller owns the frame reference.
     *
     * Returns AVERROR(EAGAIN) if filter graph requires more input.
     *
     * NOTE Frame reference belongs to the caller
     */
    AVFrame* readOutput();

    /**
     * @brief Frees resources used by FrameFilter.
     */
    void clean();
    
    /**
     * @brief Flag to know whether or not the filter graph is initialized.
     */
    bool initialized_ {false};

private:
    /**
     * @brief Initializes output of filter graph.
     */
    int initOutputFilter(AVFilterInOut* out);

    /**
     * @brief Initializes an input of filter graph.
     */
    int initInputFilter(AVFilterInOut* in, MediaStream msp);

    /**
     * @brief Reinitializes the filter graph.
     *
     * Reinitializes with @inputParams_, which should be updated beforehand.
     */
    int reinitialize();

    /**
     * @brief Convenience method that prints @msg and returns err.
     *
     * NOTE @msg should not be null.
     */
    int fail(std::string msg, int err) const;

    /**
     * @brief Filter graph pointer.
     */
    AVFilterGraph* graph_{};

    /**
     * @brief Filter graph output.
     *
     * Corresponds to a buffersink/abuffersink filter.
     */
    AVFilterContext* output_{};

    /**
     * @brief List of filter graph inputs.
     *
     * Each corresponds to a buffer/abuffer filter.
     */
    std::vector<AVFilterContext*> inputs_;

    /**
     * @brief List of filter graph input parameters.
     *
     * Same order as @inputs_.
     */
    std::vector<MediaStream> inputParams_;

    /**
     * @brief Filter graph string.
     */
    std::string desc_ {};
};
}; // namespace jami

#endif // FRAMEFILTER_H