Embed metadata into AVI header, using ffmpeg

[^rooker]

Unfortunately, it's rarely used, but even the AVI container offers ways to embed metadata directly in the file.

I'm using the tool 'FFmpeg' to do this. According to the FFmpeg documentation, the syntax is quite straightforward:

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-metadata key=value

You need to pass the full '-metadata' argument for each key/value pair.
Here's an example:

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ffmpeg -i input.avi -vcodec copy -acodec copy -metadata title="The Title" -metadata=encoded_by="Hans Stahl" output.avi

== You *must* copy the whole file:
Unfortunately, the current FFmpeg implementation cannot simply update the header data of an existing AVI file. It must read/write the whole file at least once, in order to embed the metadata.

== Available metadata fields?
According to FFmpeg's AVI-format source code, FFmpeg’s AVI muxer honors the following metadata keys and maps them to these FourCCs in the file header:

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const AVMetadataConv ff_avi_metadata_conv[] = {
  { "IART", "artist"    },
  { "ICMT", "comment"   },
  { "ICOP", "copyright" },
  { "ICRD", "date"      },
  { "IGNR", "genre"     },
  { "ILNG", "language"  },
  { "INAM", "title"     },
  { "IPRD", "album"     },
  { "IPRT", "track"     },
  { "ISFT", "encoder"   },
  { "ITCH", "encoded_by"},
  { "strn", "title"     },
  { 0 },
};

(Note: The list in the FFmpeg Metadata article in the Multimedia Wiki is outdated and does not contain all tags)

The above list only contains the metadata fields mapped to a human readable alias. If I read FFmpeg's AVI-format source code correctly, it can handle more fields:

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const char ff_avi_tags[][5] = {
  "IARL", "IART", "ICMS", "ICMT", "ICOP", "ICRD", "ICRP", "IDIM", "IDPI",
  "IENG", "IGNR", "IKEY", "ILGT", "ILNG", "IMED", "INAM", "IPLT", "IPRD",
  "IPRT", "ISBJ", "ISFT", "ISHP", "ISRC", "ISRF", "ITCH",
  {0}
};

I couldn't find an official specification of those FourCC attribute names, but thanks to the sourcecode of a "RIFF" handling library, here's a list that looks meaningful:

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ATTRIBUTE_NAMES = {
     'Archival Location' =>  'IARL', 
     'Artist'            =>  'IART',
     'Author'            =>  'IART', 
     'Comissioned'       =>  'ICSM', 
     'Comment'           =>  'ICMT',
     'Description'       =>  'ICMT', 
     'Copyright'         =>  'ICOP', 
     'Date Created'      =>  'ICRD', 
     'Cropped'           =>  'ICRP', 
     'Dimensions'        =>  'IDIM', 
     'Dots Per Inch'     =>  'IDPI', 
     'Engineer'          =>  'IENG', 
     'Genre'             =>  'IGNR', 
     'Keywords'          =>  'IKEY', 
     'Lightness'         =>  'ILGT', 
     'Medium'            =>  'IMED', 
     'Title'             =>  'INAM',
     'Name'              =>  'INAM', 
     'Number of Colors'  =>  'IPLT', 
     'Product'           =>  'IPRD', 
     'Subject'           =>  'ISBJ', 
     'Software'          =>  'ISFT', 
     'Encoding Application' =>  'ISFT', 
     'Sharpness'         =>  'ISHP', 
     'Source'            =>  'ISRC', 
     'Source Form'       =>  'ISRF', 
     'Technician'        =>  'ITCH' 
    }

Additional references:

• Supplying FFmpeg With Metadata
• abcAVI Tag: The comparison table of different tag's formats (March, 2005)
• RIFF Tags

[^rooker]

Finally, I've found an officially-looking source reference for the metadata abbreviation tags (FourCC attribute names):
http://www.exif.org/specifications.html

On page 90 (pdf-page: 96) of the Exif 2.2 specification paper, Table 29 "INFO List Chunks", shows 23 so called "Channel ID" names a description:

== JEITA CP-3451:

The INFO list chunks currently defined are given in Table 29. These pre-registered chunks are stored as ASCII text strings terminated by NULL (the final byte is '00.H').

== Table 29 INFO List Chunks:

Channel ID / Description
IARL
Archival Location. Indicates where the subject of the file is archived.
IART
Artist. Lists the artist of the original subject of the file.
ICMS
Commissioned. Lists the name of the person or organization that commissioned the
subject of the file.
ICMT
Comments. Provides general comments about the file or the subject of the file.
ICOP
Copyright. Records the copyright information for the file.
ICRD
Creation date. Indicates the date the subject of the file was created.
ICRP
Cropped. Indicates whether an image has been cropped
IDIM
Dimensions. Specifies the size of the original subject of the file.
IDPI
Dots Per Inch. Stores the dots per inch (DPI) setting of the digitizer used to produce
the file.
IENG
Engineer. Stores the name of the engineer who worked on the file.
IGNR
Genre. Describes the genre of the original work.
IKEY
Keywords. Provides a list of keywords that refer to the file or subject of the file.
ILGT
Lightness. Describes the changes in lightness settings on the digitizer required to
produce the file.
IMED
Medium. Describes the original subject of the file, such as, "computer image,"
"drawing," "lithograph," and so forth.
INAM
Name. Stores the title of the subject of the file.
IPLT
Palette Setting. Specifies the number of colors requested when digitizing an image.
IPRD
Product. Specifies the name of the title the file was originally intended for, such as
"Encyclopedia of Pacific Northwest Geography."
ISBJ
Subject. Describes the file contents, such as "Aerial view of Seattle."
ISFT
Software. Identifies the name of the software package used to create the file.
ISHP
Sharpness. Identifies the changes in sharpness for the digitizer required to produce
the file.
ISRC
Source. Identifies the name of the person or organization who supplied the original
subject of the file.
ISRF
Source Form. Identifies the original form of the material that was digitized, such as
"slide," "paper," "map," and so forth.
ITCH
Technician. Identifies the technician who digitized the subject file.

[^rooker]

I just figured out, that these EXIF metadata tags are compatible between AVIs and WAVs:
http://www.sno.phy.queensu.ca/~phil/exi ... s/WAV.html

Extracting the audio of an AVI that contains EXIF metadata into a WAV, using ffmpeg, preserves the EXIF metadata inside the newly created wavefile.
For example, you can use tools like "MediaInfo" to display the contents of the EXIF tags.