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.