有谁熟悉mp4数据结构？

Question

在哪里mp4文件的结构是它的持续时间？

Answer 1

这可能不是你的问题的答案,但它是我的:http://mediainfo.sourceforge.net/

(它有一个库,它是开源的,所以你可以检查你需要的部分)

Answer 2

请参阅https://github.com/sannies/mp4parser项目.它是一个Java库,显示mp4文件的结构.

Answer 3

据我所知 - "mp4"容器源自QuickTime原子结构.您可以阅读QuickTime文件格式的说明.

解析quicktime原子并不是什么大问题(看看atomicParsley项目).我不确定MP4,但对于MOV文件 - "mvhd"(电影标题)原子和"tkhd"(轨道标题)原子中都有"持续时间"字段.此持续时间通常是多个帧乘以"时间刻度"属性.时间尺度可以在相同的原子中找到.

Answer 4

对于Red5 MP4阅读器,我使用了"mvhd"原子,因为它包含时间刻度和持续时间字段.从原子获取持续时间将根据使用的版本而有所不同,下面您可以看到一个示例:

public long create_full_atom(MP4DataStream bitstream) throws IOException {
    long value = bitstream.readBytes(4);
    version = (int)value >> 24;
    flags = (int)value & 0xffffff;
    readed += 4;
    return readed;
}


public long create_movie_header_atom(MP4DataStream bitstream) throws IOException {
    create_full_atom(bitstream);
    if (version == 1) {
        creationTime = createDate(bitstream.readBytes(8));
    modificationTime = createDate(bitstream.readBytes(8));
    timeScale = (int)bitstream.readBytes(4);
    duration = bitstream.readBytes(8);
    readed += 28;
    } else {
        creationTime = createDate(bitstream.readBytes(4));
    modificationTime = createDate(bitstream.readBytes(4));
    timeScale = (int)bitstream.readBytes(4);
    duration = bitstream.readBytes(4);
    readed += 16;
    }
    int qt_preferredRate = (int)bitstream.readBytes(4);
    int qt_preferredVolume = (int)bitstream.readBytes(2);
    bitstream.skipBytes(10);
    long qt_matrixA = bitstream.readBytes(4);
    long qt_matrixB = bitstream.readBytes(4);
    long qt_matrixU = bitstream.readBytes(4);
    long qt_matrixC = bitstream.readBytes(4);
    long qt_matrixD = bitstream.readBytes(4);
    long qt_matrixV = bitstream.readBytes(4);
    long qt_matrixX = bitstream.readBytes(4);
    long qt_matrixY = bitstream.readBytes(4);
    long qt_matrixW = bitstream.readBytes(4);
    long qt_previewTime = bitstream.readBytes(4);
    long qt_previewDuration = bitstream.readBytes(4);
    long qt_posterTime = bitstream.readBytes(4);
    long qt_selectionTime = bitstream.readBytes(4);
    long qt_selectionDuration = bitstream.readBytes(4);
    long qt_currentTime = bitstream.readBytes(4);
    long nextTrackID = bitstream.readBytes(4);
    readed += 80;

    return readed;

}

在旁注中,我使用值来计算播放时间和fps,如下所示:

    double fps = (videoSampleCount * timeScale) / (double) duration;
    double videoTime = ((double) duration / (double) timeScale);

videoSampleCount变量来自"stsz"原子.