A couple of weeks ago, Finland took the penultimate step to get rid of
DVB-T. Since years, we had DVB-T and DVB-T2 running in parallel. The
DVB-T transponders should be shut down in 2025.
The step was to introduce a second free-to-air DVB-T2 bouquet to carry
some channels that were previously only available with DVB-T and MPEG-2.
The VDR channel search failed to find this transponder; I ran a patched
version of https://github.com/mighty-p/t2scan/pull/15/ to generate a new
channels.conf. (Is this a bug of VDR, or a feature? I remember that when
I originally set up VDR, I had to get a channels.conf from tscan or
t2scan.)
Unlike our first free-to-air DVB-T2 bouquet, which uses MPEG-4 H.264
video with AC3 audio, the second one uses H.264 video and HE-AAC audio,
also known as LATM or LOAS. This had to be explicitly enabled for my
output device: https://github.com/reufer/rpihddevice/issues/20
The HE-AAC support in rpihddevice is experimental, maybe because the
sampling rate is hard-coded as 48 kHz and the number of channels as 2.
Unlike AC3, it does not look like these parameters would be available in
any audio frame header. As far I understood from a NorDig.org
specification, the sampling rate would always be 48 kHz, but the number
of channels could be identified by something in the container,
specifically, Table 12.28 and Table 12.29 at page 164 of
https://nordig.org/wp-content/uploads/2016/03/NorDig-Unified-Requirements-ver.-3.2.1.pdf
What would have to be changed in VDR or rpihddevice or both to correctly
switch between 2-channel and 5.1-channel HE-AAC audio? This is mostly an
academic question and exercise, because I only have stereo audio
hardware and don't know if any programming is actually available with
multichannel audio.
Best regards,
Marko
