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Podcast Comparison, Part 2: MP3 Metadata (ID3 Tags)

The second post of this comparison series is about metadata in MP3 files. Metadata allows information such as the title, artist, comments, cover image and other information about the audio to be stored in the file itself. MP3 files use ID3 tags and in the following I will compare common tags, image details and ID3 versions of various popular podcasts.
The analyzed files are the same as in Podcast Comparison, Part 1: File Formats and Bitrates.

Nice open source tools to analyze MP3 metadata are for instance eyeD3, soxi, mp3diags or EasyTag.

ID3 Versions and Used Tags

There are two major versions of ID3 tags: ID3v1 and ID3v2, with various minor versions. The most popular version implemented today is ID3 version 2.3 (according to the official ID3 site), the latest one is ID3v2.4. For a list and explanation of possible ID3v2 tags see Declared ID3v2 frames.

Here is the list of podcasts with ID3 version, used tags and its encoder software:

Podcast ID3 Used Tags Encoder
CRE 188 v2.2 title, artist, album, year, genre (Podcast), Comment (for URL), TPE2 (accompaniment), TENC (encoder software) iTunes
techzing 162 v2.4 title, artist, album, composer, year, genre (Podcast), track, Comment (for URL) unknown
Hoaxilla 70 v2.4 title, artist, album, year, genre (Podcast), TPUB (publisher), Comment (for show notes), TSSE (software for encoding) Lavf52
Planet Money Podcast v1.0 title, artist, year, genre (Blues) unknown
Startups For the Rest of Us 61 v2.2 title, artist, album, year, genre (Podcast), Comment (description), Lyrics (description), TENC (encoder software) iTunes
Alternativlos 21 v2.3 title, artist, album, year, track, genre (Speech), Comment (description) unknown
Bits und so 272 v2.2 title, artist, album, year, track, genre (Podcast), Comment (for URL), TENC (encoder software) iTunes
Elementarfragen 9 v2.2 title, artist, album, year, genre (Podcast), Comment (for URL), Lyrics (for show notes), TSSE (encoding software), TDAT (date), TBPM (BPM), TIT3 (subtitles) GarageBand
Ubuntu UK Podcast v2.4 title, artist, album, year, track, genre (Podcast), Comment (for show notes), Lyrics (for show notes), TDTG (tagging time) unknown
Fanboys Podcast 49 v2.3 title, artist, album, year, TENC (encoder software) Hindenburg Journalist
This American Life 420 v2.2 title, artist, year, genre (Podcast), Comment (for copyright information) unknown
ARD Radio Tatort v2.3 title, artist, album, year, genre (Podcast), TPUB (publisher), Comment (for show notes), link frames (WCOP, WOAF, WOAS, WORS, WPUB, WXXX), TEXT (Text writer), TLAN (language), TRSN (radio station), TSRO (radio station owner) unknown
Deutschland Radio Wissen v2.3 title, artist, album, year, TCOP (copyright), link frames (WCOP, WOAF, WORS, WPUB) unknown
Freakonomics v2.3 title, artist, album, year, genre (Audio), Comment, WXXX (for URL), TCOP (copyright), TENC (encoder software), TXXX (tagging time) DigaSystem DigaPorter
OE1 Geschichte Podcast v2.3 title, artist, album, year, genre (Podcast), Comment, TCOP (copyright), TENC (encoder software), link frames (WCOP, WORS, WPUB), TOFN (original filename) lame
Wait Wait ... don't tell me v1.0 title, artist, year, genre (Blues) unknown
Radio New Zealand Afternoons v2.3 title, artist, album, Comment (for show notes), TSSE (software settings for encoding), TLEN (length) lame
Inside Home Recording 97 v2.2 title, artist, album, year, track, genre (Podcast), BPM, Lyrics (for show notes), TSSE (software settings for encoding) GarageBand
Radio Tux v2.4 title, artist, album, year, genre (Podcast), WXXX (for URL) unknown

It can be seen that iTunes and GarageBand use ID3v2.2 tags, although the recommended version is ID3v2.3 (as implemented by most public radio stations).
Mp3diags even displays a warning for v2.2 and v2.4 tags:
"No ID3v2.3.0 tag found, although this is the most popular tag for storing song information."

Nearly all podcasts use the genre "Podcast", which is not even included in the official ID3 genre list. Furthermore most unknwon encoders are probably lame.

Attached Picture

It is possible to attach pictures to an MP3 file. These images should be in jpeg or png format, they have a defined picture type (other, front cover, artist, conductor, composer, etc.) and might contain an additional description - see ID3 Attached Picture.

Here are the details about attached pictures of all analyzed podcasts which include an image:

Podcast Picture Type MIME Type Size Resolution
CRE 188 OTHER Image image/JPG 238 KB 600x600
techzing 162 OTHER Image image/png 473.8 KB 600x600
Hoaxilla 70 OTHER Image image/jpeg 98.4 KB 600x600
Startups For the Rest of Us 61 OTHER Image image/PNG 24.9 KB 271x127
Alternativlos 21 FRONT_COVER Image image/png 31.7 KB 521x491
Elementarfragen 9 OTHER Image image/PNG 55.7 KB 1024x1024
Ubuntu UK Podcast FRONT_COVER Image image/jpeg 12.3 KB 388x388
Fanboys Podcast 49 OTHER Image image/jpeg 13.4 KB 300x300
This American Life 420 OTHER Image image/JPG 20 KB 300x300
ARD Radio Tatort OTHER Image image/jpg 33.8 KB 300x300
Freakonomics FRONT_COVER Image image/jpeg 45 KB 300x300
OE1 Geschichte Podcast FRONT_COVER Image image/png 153.4 KB 300x300
Inside Home Recording 97 OTHER Image image/JPG 68 KB 300x299
Radio Tux OTHER Image image/jpeg 3.2 KB 160x160

One small detail: iTunes and GarageBand use capital letters for mimetypes (e.g. image/PNG instead of image/png). This confuses some tag readers and players, for instance the EasyTag editor is not able to display these images.

Podcast Comparison Series

If you are interested in more properties of popular podcasts, look through the other posts of the podcast comparison series:

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