MP4

Multivalue Tags

Note

not finished..

The only case where iTunes writes multiple values is the covr atom by including multiple data atoms.

For a collection of 1700 random mp4s the only place where multiple values occur is multiple ---- atoms with com.apple.iTunes:unknown as identifier.

Foobar2000 (1.3.3)

Writing:
Foobar writes single values in the official atoms and multiple values in the reverse DNS namespace. Multiple values get saved as multiple --- with the same name and one data each.
Reading:
Foobar only reads the first data atom in all child atoms in ilst and ----. Everything else gets ignored and thrown out on save.

iTunes (11.4)

Writing:
Given two \xa9gen atoms with each two data atoms. Modifying the genre modifies the first data atom of the second \xa9gen atom and it leaves the second data as is and writes is back. The first \xa9gen atom gets thrown out. If the genre gets removed in the iTunes GUI, both \xa9gen get thrown out.
Reading:
Given two \xa9gen atoms with each two data atoms it displays the first data of the second \xa9gen.

No idea how it handles --- atoms.

So, multiple values for official ilst sub atoms should be saved as multiple data because iTunes will at least not touch other values and editing/display use the first one.

Random Struct Decls

class DecoderConfigDescriptor extends BaseDescriptor :
        bit(8) tag=DecoderConfigDescrTag {
    bit(8) objectTypeIndication;
    bit(6) streamType;
    bit(1) upStream;
    const bit(1) reserved=1;
    bit(24) bufferSizeDB;
    bit(32) maxBitrate;
    bit(32) avgBitrate;
    DecoderSpecificInfo decSpecificInfo[0 .. 1];
    profileLevelIndicationIndexDescriptor profileLevelIndicationIndexDescr[0..255];
}

class ES_Descriptor extends BaseDescriptor :
        bit(8) tag=ES_DescrTag {
    bit(16) ES_ID;
    bit(1) streamDependenceFlag;
    bit(1) URL_Flag;
    bit(1) OCRstreamFlag;
    bit(5) streamPriority;
    if (streamDependenceFlag)
        bit(16) dependsOn_ES_ID;
    if (URL_Flag) {
        bit(8) URLlength;
        bit(8) URLstring[URLlength];
    }
    if (OCRstreamFlag)
        bit(16) OCR_ES_Id;
    DecoderConfigDescriptor decConfigDescr;
    if (ODProfileLevelIndication==0x01) //no SL extension.
    {
        SLConfigDescriptor slConfigDescr;
    }
    else // SL extension is possible.
    {
        SLConfigDescriptor slConfigDescr;
    }
    IPI_DescrPointer ipiPtr[0 .. 1];
    IP_IdentificationDataSet ipIDS[0 .. 255];
    IPMP_DescriptorPointer ipmpDescrPtr[0 .. 255];
    LanguageDescriptor langDescr[0 .. 255];
    QoS_Descriptor qosDescr[0 .. 1];
    RegistrationDescriptor regDescr[0 .. 1];
    ExtensionDescriptor extDescr[0 .. 255];
}

abstract class DecoderSpecificInfo extends BaseDescriptor :
    bit(8) tag=DecSpecificInfoTag
{
    // empty. To be filled by classes extending this class.
}

AudioSpecificConfig if objectTypeIndication == 0x40 and streamType = 0x5

AudioSpecificConfig extends DecoderSpecificInfo
{
    bit(5) audioObjectType;
    if (audioObjectType == 31) {
        audioObjectType = 32 + bit(6) audioObjectTypeExt;
    }

    [...]
}

audioObjectType is defined in 14496-3 1.6.2.2.1