num_channels = g_slist_length(o->sdi->channels);
g_string_append_printf(header, "Acquisition with %d/%d channels",
ctx->num_enabled_channels, num_channels);
num_channels = g_slist_length(o->sdi->channels);
g_string_append_printf(header, "Acquisition with %d/%d channels",
ctx->num_enabled_channels, num_channels);