async setVolume ({ state, dispatch }, volume) {
      const volumes = Object.keys(state.tracks)
        .map(track => dispatch('setTrackVolume', { track, volume }))

      const ids = await Promise.all(volumes)
      return ids.flat()
    }
Sets volume of all tracks

@param volume {number} volume between 0 and 1
@return Array of IDs that volume was set on