Archive for category Amateur Radio

Sony HDR-AS30V vs. ExFAT vs. Ext2 Times: Total Bafflement

I’d like to overlay a timestamp on still images extracted from Sony HDR-AS30V camera videos, ideally including the frame number, to record exactly when the incident occurred. Movie players use relative time, with 00:00:00 at the beginning of the file, so we’ll need either the file timestamp or the timestamp recorded in the image’s Exif data, plus the frame number modulo 60 (or, shudder, 59.94 for NTSC).

The ExFAT format used on 64 GB MicroSD cards stores the file’s creation time, its modification time (writing data), and the most recent access time (reading data). That’s similar to the Linux ext2/3/4 filesystem time and unlike plain old FAT, which omits the access time.

The various FAT formats store local time, with no regard for time zones, Daylight Saving Time, or anything else. Linux stores times as UTC and converts to local time on the fly. This has catastrophic consequences for getting any of this right.

It helps to have alias ls='ls -h --color=auto --time-style=long-iso' in your .bashrc file.

The HDR-AS30V has a year-month-day calendar, a 24-hour clock, a Time Zone value, and a separate DST on/off setting.

Turning DST on adds 1 hr to the Time Zone value, turning it off subtracts 1 hr. That has the side effect of changing the clock time: not what I expected. You must, therefore, set the TZ first, then DST, then the clock, which does not follow the menu’s natural order of things.

The camera sets file timestamps as it creates the files, but Linux also meddles with the values while displaying them. Some doc suggests that Linux regards FAT file timestamps as UTC and applies DST correction, which seems to match what I see. There’s a mount option (-o tz=UTC) that seems to have no effect, as well as an undocumented time offset (-o time_offset=60) that also has no effect.

Setting the TZ to GMT+0 (Sony uses GMT, not UTC) for simplicity, setting the clock to the correct local time, and twiddling DST shows that:

  • Rebooting (remove /insert battery) doesn’t change anything
  • Metadata in file = clock setting – DST setting (-1 on, +0 off)
  • MP4 / THM file create / modify times = always clock +1 hour
  • MP4 / THM file access times = as create / modify until next Linux access

Under those conditions, with the clock set to (locally accurate) 1908, UTC+1, and DST off, then the Exif timestamp metadata for a movie created at that time look like this:

exiftool /mnt/part/MP_ROOT/100ANV01/MAH00036.MP4 | grep -i date
File Modification Date/Time     : 2014:09:01 20:08:09-04:00
File Access Date/Time           : 2014:09:01 19:10:14-04:00
File Inode Change Date/Time     : 2014:09:01 20:08:09-04:00
Create Date                     : 2014:09:01 19:08:03
Modify Date                     : 2014:09:01 19:08:08
Track Create Date               : 2014:09:01 19:08:03
Track Modify Date               : 2014:09:01 19:08:08
Media Create Date               : 2014:09:01 19:08:03
Media Modify Date               : 2014:09:01 19:08:08

The corresponding filesystem values:

ll /mnt/part/MP_ROOT/100ANV01/
total 146M
... snippage ...
-rwxr-xr-x 1 ed root  14M 2014-09-01 20:08 MAH00036.MP4
-rwxr-xr-x 1 ed root 8.5K 2014-09-01 20:08 MAH00036.THM

ll -c /mnt/part/MP_ROOT/100ANV01/
total 146M
... snippage ...
-rwxr-xr-x 1 ed root  14M 2014-09-01 20:08 MAH00036.MP4
-rwxr-xr-x 1 ed root 8.5K 2014-09-01 20:08 MAH00036.THM

ll -u /mnt/part/MP_ROOT/100ANV01/
total 146M
... snippage ...
-rwxr-xr-x 1 ed root  14M 2014-09-01 19:10 MAH00036.MP4
-rwxr-xr-x 1 ed root 8.5K 2014-09-01 20:08 MAH00036.THM

The THM file contains a 160×120 pixel JPG thumbnail image taken from the first frame of the corresponding MP4 file. For longer movies, it’s more obvious that the MP4 file creation date is the start of the movie and its modification date is the end. The maximum 4 GB file size of corresponds to exactly 22:43 of 1920×1080 movie @ 60 frame/sec (the metadata says 59.94).

The +1 hour offset in the file create / modify times comes from the FAT timestamp being (incorrectly) adjusted by the Linux DST setting. When exiftool reads the MP4 file, that resets its access time to the actual time as seen by Linux, thereby crushing the bogus FAT time.

Doing the seemingly sensible thing of setting the camera to have the correct local time (roughly 1930), the correct time zone, and the correct DST setting produces this jumble:

exiftool /mnt/part/MP_ROOT/100ANV01/MAH00037.MP4 | grep -i date
File Modification Date/Time     : 2014:09:01 20:33:15-04:00
File Access Date/Time           : 2014:09:01 20:33:14-04:00
File Inode Change Date/Time     : 2014:09:01 20:33:15-04:00
Create Date                     : 2014:09:01 23:33:11
Modify Date                     : 2014:09:01 23:33:14
Track Create Date               : 2014:09:01 23:33:11
Track Modify Date               : 2014:09:01 23:33:14
Media Create Date               : 2014:09:01 23:33:11
Media Modify Date               : 2014:09:01 23:33:14

ll /mnt/part/MP_ROOT/100ANV01/MAH00037*
-rwxr-xr-x 1 ed root  11M 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.MP4
-rwxr-xr-x 1 ed root 8.2K 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.THM

ll -c /mnt/part/MP_ROOT/100ANV01/MAH00037*
-rwxr-xr-x 1 ed root  11M 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.MP4
-rwxr-xr-x 1 ed root 8.2K 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.THM

ll -u /mnt/part/MP_ROOT/100ANV01/MAH00037*
-rwxr-xr-x 1 ed root  11M 2014-09-01 19:34 /mnt/part/MP_ROOT/100ANV01/MAH00037.MP4
-rwxr-xr-x 1 ed root 8.2K 2014-09-01 20:33 /mnt/part/MP_ROOT/100ANV01/MAH00037.THM

The only correct time in that mess is in the next-to-last line: the access time for the MP4 file. Every other timestamp comes out wrong, with the internal metadata values being off by +4 hours; that suggests the camera sets the internal timestamps to UTC.

As nearly as I can figure, the only way to make this work requires setting the clock to the local time, TZ to UTC+0, and DST off. That will screw up the filesystem timestamps, but at least the Exif metadata will be correct, for some value of correct.

The camera’s GPS receiver depends on the clock for its initial synchronization. I don’t know how the TZ and DST settings affect the clock’s correctness for that purpose.

I do not know if / how / when the displayed times have been altered by the programs that display them.

I think exiftool can extract the times from the internal metadata and fix up the filesystem times, but that’ll take more tinkering.

Sheesh & similar remarks…

3 Comments

Cycling the Hudson Valley: 2014

Seven days and 300 miles of pedal pushing:

KE4ZNU route - 2014-07-28 through 2014-08-04

KE4ZNU route – 2014-07-28 through 2014-08-04

We rode north to the start of the Cycling the Hudson Valley ride in (wait for it) Hudson, rode south while crossing the Hudson six times, then I rode north from Da Bronx while the other 100 riders proceeded south to the tip of Manhattan and the finish line in Brooklyn. Mary, alas, drove the last few days to avoid aggravating a tender tendon.

While everybody else had a touristing day in Hyde Park, we slept in our own beds for two nights.

Everything you need to know about modern bicycle touring:

Cycling the Hudson Valley - Charging Station

Cycling the Hudson Valley – Charging Station

The straight line along the right side of the map, from just below the New Croton Reservoir to Hopewell Junction, represents data loss from riding in a valley, plus knocking the coaxial power plug out of the battery pack where the South County Trail becomes one with Rt 100 / Saw Mill River Road for a few miles.

That last day had plenty of hillclimbing, even on the rail trail, but with a rewarding section of Rt 52 that drops 500 feet in a mile; I hit 41 mph while passing under I-84.

A good time was had by all!

9 Comments

Bike Helmet Earbud Iteration

Based on having to seal the rear vent hole of the previous earbud, I did the same for the new one:

Earbud - blocked vent

Earbud – blocked vent

The audio quality was terrible, so I tried another bud with a foam windscreen over the hole and a hole punched in the middle of the double-sided white foam tape:

Earbud - foam over vent

Earbud – foam over vent

The audio remained unintelligible, so I tried an upscale (but still cheap, because surplus) Koss earbud, first without blocking the vents and then with snippets of Kapton tape:

Koss earbud - tape over vent

Koss earbud – tape over vent

The earphone has three slits on each side, but only the middle slit has a hole penetrating the case; it must be a stylin’ thing.

That sounded better, so I’ll roll with it. There’s supposed to be a foam cover over the housing, but those things always get grody and fall off; there’s not much point.

As nearly as I can tell, contemporary earbud designs optimize for volume (dBm/mV) and thumpin’ bass, all to the detriment of actual audio quality. Based on numerous samples over the years, there is zero correlation between price (admittedly, on the low end) and audio quality (admittedly, with my crappy hearing).

I own a pair of very nice (and thoroughly obsolete) Shure E2c sound-isolating ear beetles that sound great (even with my crappy hearing), but I’m unwilling to chop them up for the bike headset …

Leave a comment

Bike Helmet Boom Mic: Assembly

After building the mic mount, another dab of epoxy mounted the length of AWG 10 wire I said I wouldn’t use:

Bike Helmet Mic Boom - rod epoxy

Bike Helmet Mic Boom – rod epoxy

The whole point of the complex mount is to expose the two noise cancelling holes on the back of the electret element:

Bike Helmet Mic - electret element rear

Bike Helmet Mic – electret element rear

Add heatstink tubing over the entire length of the boom wire, use more black cable ties, shape another foam ball:

Bike Helmet Mic Boom - installed

Bike Helmet Mic Boom – installed

And it worked on the first try, not that there’s much to it.

Yeah, that’s the HDR-AS30V camera mount up top: dork mode in full effect.

Leave a comment

Bike Helmet Boom Mic: Housing

The last time around, this involved silver soldering the boom wire directly to the mic housing. This time, I filed a fishmouth in the smaller tube and epoxied it to the tube that’ll hold the mic capsule:

Bike Helmet Mic Boom - housing

Bike Helmet Mic Boom – housing

The smaller tube is a loose slip fit for #10 copper wire, but that’s really too heavy for the boom. I’ll probably nestle #12 wire inside another tube and epoxy that whole affair in place.

The mic capsule tube needs a rounded notch filed in one end to accommodate the wire.

Leave a comment

Monthly Image: Hudson River Boating

Much of the boat traffic on the Hudson consists of barges shuttling bulk commodities between the Atlantic and the Port of Albany. I think this is a crude oil barge, based on the Christmas Tree plumbing that was more visible when it passed under the Mid Hudson Bridge:

Walkway and Barge - from Mid Hudson Bridge

Walkway and Barge – from Mid Hudson Bridge

We crossed the Walkway Over the Hudson westbound, where a work crew was tending a crane. That’s how they do repair and inspection:

Walkway Inspection Crane - from Mid Hudson Bridge

Walkway Inspection Crane – from Mid Hudson Bridge

The Hudson River has far fewer power boats than in years gone by, probably due to their gallon-per-minute fuel consumption:

Power boat on Hudson River - from Mid Hudson Bridge

Power boat on Hudson River – from Mid Hudson Bridge

It was a fine day for a ride:

KE4ZNU - APRS track 2014-06-30

KE4ZNU – APRS track 2014-06-30

4 Comments

3D Printed Things I’ve Designed: Brag Sheets

The whole reason I got a 3D printer in the first place was to make things that would otherwise be too difficult or tedious by hand or on a CNC mill. Most of the things I make look like brackets and I don’t do sculptures … this stuff solves problems!

Being able to go from “I need a part shaped like that” to holding the thing in my hand a few hours (or, for complex designs, days) later is empowering. Being able to adjust a dimension by changing the source code and “recompiling” to get a new part is wonderful.

These five slides from the presentation show my answers to the question “Why would anyone want a 3D printer?” Clicky for more dots.

Things I Designed - 1

Things I Designed – 1

Things I Designed - 2

Things I Designed – 2

Things I Designed - 3

Things I Designed – 3

Things I Designed - 4

Things I Designed – 4

Things I Designed - 5

Things I Designed – 5

You can find those and more by searching for OpenSCAD source code.

They go along with the sheets of solid models.

, ,

2 Comments