Tag Archives: mp3

Recently Eyal Mozes hired me to determine why the sound system in his new Honda Civic wouldn’t play some MP3 files. This was a chance to do some interesting investigative work, and I’ve found what I think is a previously unidentified product defect.

He sent me twenty MP3 files, ten of which would play on his system and ten of which wouldn’t. First I ran some preliminary tests, establishing that iTunes, QuickTime Player, Audacity, and even my older Honda stereo had no trouble with the files. Then I ran Exiftool on them and looked at the output to see what the difference was.

The first thing I looked for was variable bitrate encoding, which is the most common cause of failure to play MP3 files. None of them used a variable bitrate. Looking more closely, I saw that all the files had both ID3 V1 and V2 metadata. This is legitimate. In the files he’d indicated as non-playable, though, the length of the ID3 V2 segment was zero. This was true in all the non-playable files, while all the playable ones had ID3 V2 with some data fields. I verified with a hex dump that the start of the files was a ten-byte empty ID3 V2.3 segment.

I continued looking for any other systematic differences, but that was the only one I found. It’s highly likely that the MP3 software in Eyal’s car — and, therefore, in many Hondas and maybe even other makes — has a bug that makes a file fail to play if there’s a zero-length ID3 V2 segment. (Update: Just to be clear, this is a legitimate if unusual case, not a violation of the format.)

Eyal had gone to arbitration to get his vehicle returned under the warranty; Honda’s response was unimpressive. Initially, he told me, Honda claimed that the non-playing files were under DRM. This is nonsense; there’s no such thing as DRM on MP3 files. They withdrew this claim but then asserted that “compatibility issues” related to encoding were the problem, without giving any specifics. The ID3 header in an MP3 file is unrelated to the encoding of the file, and I didn’t see any systematic differences in encoding parameters between the playable and non-playable files. Honda claimed to be unable to tell how the files were encoded. They may not have been able to tell what software was used, but the only “how” that’s relevant is the encoding parameters.

This problem won’t make your brakes fail or your wheels fall off, but Honda should still treat it as a product defect, come up with a fix, and offer it to customers for free. If they can upgrade the firmware, that’s great; if not, they’ll have to issue replacement units. The bug sounds like one that’s easy to fix once the programmers are aware of it. The testing just wasn’t thorough enough to catch this case.

If anyone wants to hire me for more file format forensic work, let me know. This was fun to investigate.