Modern Containers

Question 1

MP4 files

Answer 1

An extensive container file

Does not define a strict structure and allows custom structure and hierarchy for each media type

Divided into media related data (audio/visual) and the metadata (timestamps, random access points)

Question 2

Box names

Answer 2

Boxes within the mp4 generally have a four letter box name referred to as the FourCc (character code)

Question 3

fytp

Answer 3

File type box

Parent standard for mp4 container

32 bytes:
-4 indicate size
-4 indicate fytp header
-4 indicate major brand (isom)
-4 indicate minor version

Compatible brands are an array of four-byte elements until end of fytp box

16 bytes remain in box size so we expect four compatible brands

Question 4

free

Answer 4

Box type

Irrelevant, can be ignored

Question 5

mdat

Answer 5

Media data box

There will be an mdat box for each media stream in file (video, audio, text)

Question 6

moov

Answer 6

Movie box type

Provides metadata which applies to entire file

Several boxes nested within moov box:
mvhd - movie header
trak - track boxes
edts - box which contains elst (edit list boxes)

Question 7

mvhd

Answer 7

Box that contains metadata

Creation time
Modification time
Timescale
Duration
Rate
Volume
Matrix
NexttrackID

Question 8

trak

Answer 8

A box contained by the moov that represents a single track of a presentation (audio, visual, text)

Each track is independent from the other tracks

Contains media data (in mdia box) and packetizatioj info for hint tracks

Question 9

tkhd

Answer 9

Trak header box

Placed within the trak box and there can only be one; contains the metadata that describes the characteristics of a single track

Question 10

Track width and height

Answer 10

Each a 32-bit fixed-point number that specifies the width/height of a track in pixels

Question 11

edts

Answer 11

Edit box

Defines portions of the media that are to be used to build a track for a movie

Contains elst box, contained in moov

Question 12

elst

Answer 12

Edit list

Box that maps from time in a movie to a time in a media

32-bit values, grouped into entries containing three values each:
-track duration (4 bytes)
-media time (4 bytes)
-media rate (4 bytes)

Question 13

Bit

Answer 13

Binary digit

0 or 1

Question 14

Byte

Answer 14

8 binary digits (8 bits)

Question 15

Nibble

Answer 15

Four binary digits (4 bits)

Question 16

stsd

Answer 16

Box which contains info about how the multimedia stream is encoded (the codec)

Contained in the moov box

Question 17

ISO/IEC

Answer 17

Intl organization of standards/intl electrotechnical commission

Standards for codecs and containers