MP3CK(1) BSD General Commands Manual MP3CK(1)NAMEmp3ck — MPEG stream consistency check
SYNOPSISmp3ck [-dhpqsv] file ...
DESCRIPTION
The MPEG Layer 3 (MP3) format is widely used to exchange digital audio
data over local networks and the Internet. Unfortunately, data transfers
may be aborted due to various events in the network or at the local
machine. Further, restarting an aborted transfer may corrupt data
because of bugs in the software. It is often hard to tell by eye or ear
whether an MP3 file that came from a third party had suffered from such a
problem in the past.
The mp3ck utility can check the consistency of an MPEG Layer 2 or 3
stream. The primary accent of the check is on the seamless flow of
frames and tags since most MPEG defects introduced by aborted network
transfers manifest theirselves in breakage of the flow.
The following options are available:
-d Ultimate verbosity. Besides all possible warnings and per-file
information, messages will be printed for every frame or tag pro‐
cessed.
-h Print a short help message and exit.
-p Be pedantic about MPEG stream inconsistencies. See the list of
detected inconsistencies for details.
-q Decrease verbosity by one level. If specified once, warnings about
trailing junk will be suppressed. If specified twice, it will cur‐
rently be equivalent to the -s option.
-s Be silent completely.
-t Try to print time offsets (MM:SS) instead of byte offsets in diagnos‐
tic messages. In a couple of messages, offsets may still be in bytes
though.
-v Increase verbosity by one level. If specified once, per-file infor‐
mation about MPEG parameters will be printed. If specified twice, it
will currently be equivalent to the -d option.
DIAGNOSTICS
Exit status is 0 if no errors occurred and no MPEG stream inconsistencies
were found. Exit status is 1 if MPEG stream inconsistencies were found.
What is considered an inconsistency can be affected by the -p option.
Exit status is 2 if a file or system error occurred.
The following MPEG stream inconsistencies are detected:
empty file A MPEG stream appeared to be of zero length.
no audio frames A byte stream contained no valid MPEG frames. This
error is likely to appear if mp3ck was invoked on a non-MPEG file.
leading junk A MPEG stream did not begin with a valid frame or ID3 tag.
In the case of a file, this is usually a sign of corruption, e.g., due to
a poorly resumed transfer over a network when the beginning of the stream
was lost.
trailing junk A MPEG stream was consistent (unless other warnings were
issued), but some random bytes appeared after its last frame. This is
mostly harmless and may be caused by an unaligned ID3v1 tag or some sort
of application-specific data. No MPEG stream inconsistency will be
reported in exit status unless the -p option was specified.
trailing junk (truncated ID3v%c tag?) The same as above, but there were
only one or two extra bytes that looked like the beginning of an ID3 tag.
"I", "ID", "T", and "TA" are the possible values for the bytes.
last frame incomplete
unexpected EOF at frame header+n
ID3v%c tag incomplete These are the most common defects seen in MPEG
files. They appear when an aborted transfer over a network remains unno‐
ticed. However, a uniform or slightly varying number of bytes missing
from the last frame over a series of files is usually just a sign of a
quirk of the MPEG encoder/tagger used.
sync after %ld bytes of junk Normal flow of MPEG frames and ID3v2 tags
was broken and then resumed after a portion of random bytes. Such a
defect is likely to appear if a network transfer was resumed poorly. In
particular, many Windows FTP clients tend to lose data when resuming an
FTP upload because they fail to determine how many bytes have been deliv‐
ered to the remote side successfully. On the other hand, such a warning
appearing after an ID3v2 tag is often harmless and just indicates non-
compliant padding of the tag.
ID3v1 in the middle of the file An ID3v1 tag should not appear in the
middle of a MPEG stream. An obscure corruption of the stream is likely
to have happened.
ID3v2.%d.%d unsupported A MPEG stream contained an ID3v2 tag, but its
major version was not recognized. Since the ID3v2 standard is still
under development, its future versions may introduce features incompati‐
ble with former specifications. An unsupported ID3v2 tag is just skipped
as junk bytes.
Additionally, a number of invalid MPEG header field values are detected
and reported accordingly.
BUGS
The mp3ck utility synchronizes to a stream at byte level despite MPEG
streams being bit oriented. Byte level synchronization is sufficient for
conventional MPEG audio files.
The mp3ck utility cannot check Layer 1 streams.
ID3 tags are accepted in a Layer 2 stream.
A CRC check of MPEG headers is not implemented yet.
This manpage fails to distinguish files from streams. Can you?
BSD November 24, 2001 BSD
