Replace screenrecord execution by manual screen encoding using the
MediaCodec API.
The "screenrecord" solution had several drawbacks:
- screenrecord output is buffered, so tiny frames may not be accessible
immediately;
- it did not output a frame until the surface changed, leading to a
black screen on start;
- it is limited to 3 minutes recording, so it needed to be restarted;
- screenrecord added black borders in the video when the requested
dimensions did not preserve aspect-ratio exactly (sometimes
unavoidable since video dimensions must be multiple of 8);
- rotation handling was hacky (killing the process and starting a new
one).
Handling the encoding manually allows to solve all these problems.
