[time-nuts] Timestamps in audio files?

Jim Lux jimlux at earthlink.net
Mon Dec 21 15:22:29 UTC 2015


On 12/21/15 3:19 AM, Tim Shoppa wrote:
> As an adjunct to the thread about timestamped samples of LORAN
> transmissions...
>
> Are there any standard consumer-type audio file formats, that support
> absolute time time/datestamps? Would not have to be done continuously, but
> something like a time and date stamp inserted nearest each sample on a
> second boundary.
>
> I have worked with some analog tape audio formats in the past where
> IRIG-type timestamps were written on a separate channel or on a subcarrier.
>
> I know of many proprietary digital recording applications that make WAV's
> or MP3's or proprietary codec formats, where the filename includes a
> timestamp. Much more interested in standard formats where the timestamp is
> embedded in the file itself.
>

For RF recordings, VITA49 has a standard for timestamps in the packet 
headers (4 flavors of epoch, multiple flavors of time format and precision)

Video file formats seem to draw from older time code things like SMPTE 
and are "relative" (so you're always fooling around trying to figure out 
the offsets).  I spent a few days earlier this year trying to put 
absolute time subtitles on video files using all manner of tools, and it 
was frustrating (ffmpeg, vlc, etc.. all were to no avail).  Trying to 
put UTC time into embedded timecode was also pretty unproductive (most 
tools don't like to see the first frame occurring at a time very 
different from 00:00:00:00)


In fact, in the music file world (e.g. MIDI) you see references to 
absolute and relative time, and there, they are really talking about 
time measured in seconds vs time measured in beats; e.g. whether the 
duration of something  is 1 second, or 2 quarter notes, which might be 
the same if the tempo is 120bpm.


You might look for solutions for people trying to synchronize multiple 
multimedia streams delivered over the internet (e.g. slides and 
accompanying narration or music) because they actually have a need for 
"show this slide at time HH:MM:SS and play this sound at HH:MM:SS" kind 
of synchronization.

I suspect, though, that this kind of info gets encapsulated in the 
transport layer, rather than the underlying files holding the info.






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