SetFPS.java

package org.jcodec.movtool;
import java.lang.IllegalStateException;
import java.lang.System;


import org.jcodec.common.logging.Logger;
import org.jcodec.common.model.RationalLarge;
import org.jcodec.common.tools.MainUtils;
import org.jcodec.common.tools.MainUtils.Cmd;
import org.jcodec.containers.mp4.boxes.MovieBox;
import org.jcodec.containers.mp4.boxes.MovieFragmentBox;
import org.jcodec.containers.mp4.boxes.TimeToSampleBox;
import org.jcodec.containers.mp4.boxes.TimeToSampleBox.TimeToSampleEntry;
import org.jcodec.containers.mp4.boxes.TrakBox;

import java.io.File;

/**
 * This class is part of JCodec ( www.jcodec.org ) This software is distributed
 * under FreeBSD License
 *
 * Changes FPS on an MP4 file.
 *
 * @author Stan Vitvitskyy
 *
 */
public class SetFPS {
    private static final int MIN_TIMESCALE_ALLOWED = 25;

    public static void main1(String[] args) throws Exception {
        Cmd cmd = MainUtils.parseArguments(args);
        if (cmd.argsLength() < 2) {
            MainUtils.printHelpNoFlags("movie", "num:den");
            System.exit(-1);
        }
        final RationalLarge newFPS = RationalLarge.parse(cmd.getArg(1));

        new InplaceMP4Editor().modify(new File(cmd.getArg(0)), new MP4Edit() {
            @Override
            public void apply(MovieBox mov) {
                TrakBox vt = mov.getVideoTrack();
                TimeToSampleBox stts = vt.getStts();
                TimeToSampleEntry[] entries = stts.getEntries();
                long nSamples = 0;
                long totalDuration = 0;
                for (TimeToSampleEntry e : entries) {
                    nSamples += e.getSampleCount();
                    totalDuration += e.getSampleCount() * e.getSampleDuration();
                }

                int newTimescale = (int) newFPS.multiply(new RationalLarge(totalDuration, nSamples)).scalarClip();
                if (newTimescale >= MIN_TIMESCALE_ALLOWED) {
                    // Playing with timescale if possible
                    vt.setTimescale(newTimescale);
                } else {
                    // Playing with actual sample durations
                    double mul = new RationalLarge(vt.getTimescale() * totalDuration, nSamples).divideBy(newFPS)
                            .scalar();
                    Logger.info("Applying multiplier to sample durations: " + mul);
                    for (TimeToSampleEntry e : entries) {
                        e.setSampleDuration((int) (e.getSampleDuration() * mul * 100));
                    }
                    vt.setTimescale(vt.getTimescale() * 100);
                }

                if (newTimescale != vt.getTimescale()) {
                    Logger.info("Changing timescale to: " + vt.getTimescale());
                    long newDuration = totalDuration * mov.getTimescale() / vt.getTimescale();
                    mov.setDuration(newDuration);
                    vt.setDuration(newDuration);
                } else {
                    Logger.info("Already at " + newFPS.toString() + "fps, not changing.");
                }
            }

            @Override
            public void applyToFragment(MovieBox mov, MovieFragmentBox[] fragmentBox) {
                throw new RuntimeException("Unsupported");
            }
        });
    }
}