That thrill.

Lately I’ve been working with a lot of technologies that are a bit outside of my comfort zone of hardware and low level stuff. Javascript, html-y things and node.js.  At first it was a tad difficult to wrap my head around all that asynchronism and things like hoisting and what is the value of ‘this’ here. And inheritance.

Then, out of a sudden I had an epiphany and I wrote a truly marvellous piece of software. Now I can use Backbone.io on the browser and the server, the same models and codebase on both without a single change. Models are automatically synchronized. On top of that there’s a redis transport so I can sync models between different node instances in real time without hitting the storage (mongo in this case). And the icing of the cake is that a python compatibility module is about to come.

The bragging tax.

This is no news but I don’t get people. I really don’t.

When a potential client approached me for a quote normally I gave two estimates. One if I am allowed to write something about it and another one (substantially higher) if they refuse.

I never said a word about open sourcing it, naming names or something like that.

Most of the time I explain, as politely as I can, that nobody is going to ‘steal’ they wonderful idea. And also that it is just a very simple variation on stuff found on textbooks and, the only original thing they did was to put a company logo on it.

It is such a shame that I honour my word in these cases.

Modifying microphone directivity.

So, we have some Logitech C920 cameras. They are really good for their price and sport a couple of microphones with echo cancellation and an omnidirectional pattern. Which is quite great for its intended use but a major pain if what you want to perform voice activity detection. Basically, all the cameras trigger when someone speaks. It can be worked around but things are a lot easier when the sound from one camera doesn’t leak that much into the others.

Not wanting to replace or modify the internal microphone array if there was another way I decided to test if with some absorbent foam the response could be shaped to something more useful.

Utilísima un poroto.

I cut a couple of rectangular prisms with cavities that more or less match the shape of the cameras. My supply of plushy fabric was rather limited and so I planned a bit more carefully how to divide it and make the crevices. After that I just cut it in four equal pieces and held everything with hot melt glue and some stitches.

Results.

I don’t have proper facilities like an anechoic chamber. Testing was done using a 1KHz tone and recording the sound from the back, 45 and 90 degrees ccw (shouldn’t matter) and facing the front of the camera. While there’s an improvement over the original pattern, the directivity achieved is not enough so we’ll pursue an alternate way of capturing sound (either a multichannel soundcard or modifying the internal mics).

Debugging USB3.0 issues when dealing with USB2.0 devices

Some time ago we needed to connect as many usb cameras as possible to a single computer and capture full hd video and audio. Most of our systems despite having a lot of connectors on the inside they really have one host controller and a hub.

While the available bandwidth may be more than enough using a compressed format the amount of isochronous transfers is rather limited. Our minimal use case called for three C920 cameras. On a normal system (one host controller behind a hub) the best we could achieve was two at 1280×720@30fps with audio and a third without audio, and only one at 1920×1080@30fps with audio.

So, we need to add more controllers. Usb 2.0 add-on cards are a thing of the past but luckily they were replaced with the faster USB3. Most of the usb 3 controllers also feature an usb 2.0 controller and hub for older devices but some (very rare) have a dedicated usb 2 controller for each port.

Given this I went ahead and bought two cards of different brand and different chipset each.

One of them had a NEC PD720200. It worked like a charm but sadly only has one usb 2 controller.

The other sported a VIA VL800. This one has one usb 2 controller per port (this can be seen with lsub -t). That lovingly discovering didn’t last for too long as the controller crashed all the time, at best it would stop responding but sometimes it locked my system hard. The guys at Via have a very interesting definition of meeting the specs. I’ve spent a whole weekend patching kernels trying to make it behave. Now I have a quite expensive and sophisticated paperweight.

Testing procedures:

I ssh’d to the target machine and ran in several consoles:

– watch -n1 ‘dmesg | tail -n 16’ to have a log should the system crash hard.

– watch -n1 ‘grep Alloc /sys/kernel/debug/usb/devices’ to monitor bus usage.

– 3x gst-launch-1.0 v4l2src device=[camera] ! queue ! ! fakesink sync=true alsasrc device=[camera soundcard] ! queue ! fakesink sync=true to capture from each device. video_caps is something like “image/jpeg,width=1920,height=1080,framerate=30/1” but I tried a couple more.

It is really wonderful how much computing power we have nowadays. The first time I compiled a kernel it took a good four hours. On my current machine (not quite new…) it takes about forty minutes from a clean tree and around ten from an already compiled one.

debugging_usb3-0

Olvidando. Otra que Patrick.

Hace unos días leí en algún lado que cuando te aferrás a una persona y no la dejás ir hacés cosas como atesorar cada sms, mail, etc…

Anteayer me senté sobre el celular, la pantalla se quedó negra y no hacía nada. Saco la batería y lo vuelvo a encender. Perdí todos los mensajes y borradores. Perdí el mensaje que me mandaste después la primera noche en que nos conocimos en el 2008. Historia para otro día si encuentro una forma de anonimizarla.

Preciso olvidar, pero a otra persona.

Voyeur

Estamos los dos juntos,  cada uno en su mundo, pero mas unidos que nunca.

“che no doy mas del sueño, me duermo un rato” – Le digo, y me recuesto sobre su espalda para dejarme llevar hacia un agradable y profundo sopor.

Como si nada sigue chiqui que chiqui tejiendo. Mas tarde (horas quizás?) vuelvo en mí, si bien tengo los ojos cerrados creo percibir todo. Estás haciendo otra cosa. Me quedo escuchando mesmerizado, sabiendo que no te percataste de que estoy pendiente de tus acciones.

Justo cuando decido por fin despertar comenzás a moverte y me acomodás suavemente contra el respaldo. Siento tu respiración recorriéndome el cuello para luego cesar abruptamente. Seguís ahí?

“hola.”

Abro los ojos y te encuentro.

Esta semana me dijeron…

“no es cuestión de casarse con el primer gil que se te cruza” (parafraseando la canción, pero debo ser el tercero o cuarto a esta altura…)

“te voy a hacer la mister té” – La misma petisa cocorita hincha de All Boys del otro día.

Hoy programo porque estoy deprimido.

Hoy programo, un módulo para MLT Framework que permite vincular varias instancias de melt usando el mismo protocolo que shmsink / shmsrc de GStreamer. Un plugin para ingresar material de melt en un pipeline de gst.

Descubrí que hace rato no tengo el área del cerebro para entender multithreading. Descubrí que todos los frameworks / librerías de vídeo en su interior albergan los mas oscuros y horribles secretos (aunque algunas no se esfuerzan en ocultarlos mucho). Por suerte el hardware es barato, no sé por qué me esfuerzo en hacer algo zerocopy si total vos lo vas a copiar de gusto cuatro o cinco veces.