I’ve been struggling recently with transcoding media files and streaming to Chromecast. Starting with the excellent project castnow over on github I wanted to be able to 1) stream media files directly from rar archives, and 2) create a web interface to start media files. It is not meant to be overly ambitious but just something useful to use at home.

Among several problems I’ve encountered so far, one has been especially annoying and turned out to have a very simple fix. The transcoding is done using ffmpeg. What I’ve been doing is to let ffmpeg reencode any media file I give it, into an mp4 with h264 and aac. This works most of the time, however for some mkv-s there’s been no image when transcoded. Casting the mkv directly to the chromecast gives you moving pictures, but it has no sound (since Chromecast does not support 5.1 audio as of yet as far as I understand).

The first attempt at a solution was to then not reencode the video but to simply copy the original. That is simple using ffmpeg flag: -vcodec copy. Unfortunately this still doesn’t work. However encoding the video to a file and then casting the file to the chromecast works. Thus there was something going on when the output from ffmpeg is streamed directly. I’ve still not worked out what is going on, but I’ve found a solution. Instead of creating a mp4 container, encoding everything into a mkv (or matroska) suddenly makes everything work just fine. The final line is

cat some-media-file | ffmpeg -i - -f matroska -vcodec h264 -acodec aac -ac2 pipe:1 | stream-to-chromecast

So far this seems to work all the time, however it is somewhat unnecessary to encode h264 if the video is already h264. In my project I therefor check codecs and set the flags for ffmpeg accordingly.

The project is written in Node.JS and is available on the following github repository.

Today I was invited to give a talk at the Mobile Apps Group Meetup in Glasgow. I decided to talk briefly about my own app development in my research, why it involves quickly building apps, and how I tend to do that.

I first gave the premise of my work: To understand an app (or the ideas manifested in the app), it needs to be built, so that it can be studied in use. In my view, we can only know what an artefact is once it is in use. We cannot know what it is prior to that.

I then explained how I suggest people to do that. None of the points are anything new, but it is hopefully something that people will start doing once they hear it often enough so I figured it is worth talking about. Concisely I’m trying to convey that you should make decisions when they are easy to make and refrain from it when it is time consuming.

Thus the process is:

• Sketch a lot of ideas. Sketch on paper or in any other material that is easy to produce and easy to discard.
• Make a mockup using Sketch, Photoshop, or anything else that allow you to create what you want different screens of your app should look like. This is where decisions are made. From the sketches made previously, pick one, make it into images that will say exactly what the app will look like on screen. The purpose of this mockup is to describe what is to implemented in the next phase.
• Now you build. But make no decisions what so ever. Just transfer the decisions manifested in the mockups, down to the font sizes, margins, and colours. As soon as you start playing around with margins, font sizes, and colours, you start loosing a lot of time. The reason is because it is not as easy and efficient as it would have been if you would have done this already when creating the mockups, so you should not do it now! If it makes it easier, pretend that the mockups come from a paying customer who pays you to implement an app that looks exactly like he has decided and you have no room for creative suggestions.

In my experience, following this simple rule of making all decisions while creating the mockups, and making no decisions when implementing, makes implementing it a breeze. I think one of the reasons for this is because when you try to make decisions in the implementation phase you not only need to think about how you would like it to look, but you also need to think about how to make it so. Having the decision made means you only need to think about how to make it.