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The TfhdBox and related fields encapsulate defaults for per sample metadata in the fragment. The syntax of the TfhdBox field is a strict subset of the syntax of the Track Fragment Header Box defined in [ISO/IEC-14496-12].

TfhdBox (variable): Metadata container for per sample defaults.

TfhdBoxLength (4 bytes): The length of the TfhdBox field, in bytes, including the TfhdBoxLength field. If the value of the TfhdBoxLength field is %, the TfhdBoxLongLength field MUST be present.

TfhdBoxLongLength (8 bytes): The length of the TfhdBox field, in bytes, including the TfhdBoxLongLength field.

BaseDataOffset (8 bytes): The offset, in bytes, from the beginning of the MdatBox field to the sample field in the MdatBox field.

SampleDescriptionIndex (4 bytes): The ordinal of the sample description for the track that is applicable to this fragment. This field SHOULD be omitted.

DefaultSampleDuration (4 bytes): The default duration of each sample, in increments defined by the TimeScale for the track.

DefaultSampleSize (4 bytes): The default size of each sample, in bytes.

DefaultSampleFlags (4 bytes): The default value of the SampleFlags field for each sample.

The syntax of the fields defined in this section, specified in ABNF [RFC5234], is as follows:

TfhdBox = TfhdBoxLength TfhdBoxType [TfhdBoxLongLength] TfhdBoxFields                                                          
TfhdBoxType = %d116 %d102 %d104 %d100                                                          
TfhdBoxLength = BoxLength                                                          
TfhdBoxLongLength = LongBoxLength                                                          
TfhdBoxFields = TfhdBoxVersion                                                          
                [ BaseDataOffset ]                                                          
                [ SampleDescriptionIndex ]                                                          
                [ DefaultSampleDuration ]                                                          
                [ DefaultSampleSize ]                                                          
                [ DefaultSampleFlags ]                                                          
TfhdBoxVersion = %x00                                                          
TfhdBoxFlags = 18*18 RESERVED_BIT                                                           
BaseDataOffset = UNSIGNED_INT64                                                          
SampleDescriptionIndex = UNSIGNED_INT32                                                          
DefaultSampleDuration = UNSIGNED_INT32                                                          
DefaultSampleSize = UNSIGNED_INT32                                                          
DefaultSampleFlags = SampleFlags                                                          
TfhdBoxChildren = *( VendorExtensionUUIDBox )
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